Introduction

If you work with SQL Server as a DBA, SQL Developer, Database Developer, Data Engineer, Database Architect, or database professional, you will eventually encounter an error message that stops your query, application, deployment, backup, restore, or production workload.

And when that happens, the first reaction is often:

“Let me Google this error.”

Or today:

“Let me ask AI what this error means.”

Those tools are useful, but you shouldn’t have to start from zero every time.

This SQL Server & DBA Error Codes Cheat Sheet is designed as a practical reference that you can bookmark and keep available while working with SQL Server.

It covers 100+ commonly encountered SQL Server, DBA, performance, security, storage, backup/restore, connectivity, and Azure SQL errors.

For each error, the goal is to answer five questions:

1. What does the error mean?
2. Why does it happen?
3. What should I check first?
4. What should I do next?
5. How serious is it?

Please Note: An error number alone is not always enough to diagnose a problem. Always capture the complete error message, state, severity, database, procedure, line number, and surrounding context. Microsoft documents these attributes as important parts of SQL Server error information.

SQL Server Error Severity

Before looking at individual errors, understand the basic severity levels.

Severity	General Meaning
0–10	Informational messages
11–16	User/programming or correctable errors
17–19	Resource/software errors that may require DBA attention
20–24	Serious errors that may affect the connection or database
25	Fatal/system-level condition

Severity alone doesn’t determine how serious an incident is. The error number, state, frequency, impact, and environment also matter.

100+ SQL Server & DBA Error Codes Cheat Sheet

1. SQL Syntax, Object & Query Errors

Error	Meaning	Why It Happens	First Check	Solution / Next Step
102	Incorrect syntax near…	T-SQL syntax is invalid	Statement around the reported location	Correct syntax
105	Unclosed quotation mark	String quotation is not closed	SQL text	Close the quotation or fix dynamic SQL
109	INSERT column/value mismatch	Number of values doesn’t match columns	INSERT statement	Match columns and values
110	Too many values	More values supplied than expected	INSERT statement	Correct column/value list
111	CREATE PROCEDURE must be first statement in batch	Procedure definition isn’t first in batch	Batch structure	Separate with GO or use separate batch
113	Comment not terminated	/* ... */ isn’t closed	SQL script	Close the comment
156	Incorrect syntax near keyword	Invalid syntax around a T-SQL keyword	SQL statement	Review syntax
207	Invalid column name	Column doesn’t exist or name is incorrect	Table/schema/column	Verify column and aliases
208	Invalid object name	Table/view/procedure doesn’t exist in current context	Database/schema/object	Verify database and schema
209	Ambiguous column name	Same column name exists in multiple referenced objects	JOIN/query	Qualify column with alias
213	Column/value mismatch	INSERT doesn’t match table definition	INSERT	Specify target columns explicitly
2714	Object already exists	Object with same name already exists	Object name	ALTER, DROP, or rename appropriately
2812	Could not find stored procedure	Procedure doesn’t exist in current database/schema	Procedure name	Verify database and schema
8120	Column invalid in SELECT list because not contained in GROUP BY	Aggregation/GROUP BY problem	SELECT and GROUP BY	Add column to GROUP BY or aggregate it
8622	Query processor unable to produce plan	Hints/restrictions prevent valid plan	Query hints and indexes	Remove inappropriate hints and retest
8623	Query processor ran out of internal resources	Query is too complex for available optimizer resources	Query complexity	Simplify/rewrite query
8630	Internal query processor error	Query optimizer encountered an internal condition	Error log and SQL version	Investigate and check current updates/CUs

2. Data Type & Conversion Errors

Error	Meaning	Why It Happens	First Check	Solution
245	Conversion failed when converting data type	Value cannot be converted to target type	Source values and data types	Validate input or use appropriate conversion
241	Conversion failed when converting date/time	Invalid date/time value	Input date	Correct date format/value
242	Date/time conversion resulted in out-of-range value	Date is outside valid range	Date expression	Validate date calculation
257	Implicit conversion not allowed	SQL Server cannot perform required conversion	Data types	Use compatible types or explicit conversion
295	Data conversion error	Value cannot be converted	Input data	Validate source data
8114	Error converting data type	Conversion failed	Source and destination types	Correct conversion
8115	Arithmetic overflow	Value exceeds data type range	Numeric value/type	Use larger appropriate data type
8116	Argument data type invalid	Function doesn’t accept supplied type	Function arguments	Use supported data type
8117	Operand data type invalid	Operation isn’t supported for the type	Expression	Correct data types
8134	Divide by zero	Denominator is zero	Calculation	Handle zero using validation or NULLIF()
8144	Too many parameters	Procedure/function received extra parameters	EXEC statement	Match parameters with definition
8146	Procedure has no parameters	Parameters supplied to procedure that accepts none	EXEC statement	Remove unnecessary parameters
535	Date/time difference overflow	Date calculation exceeds supported range	DATEDIFF/date expression	Use appropriate data type or calculation
8118	Operand/data type issue	Invalid operation involving data types	Expression	Check data types and implicit conversions

Example: Avoiding divide-by-zero

SELECT
    SalesAmount / NULLIF(Quantity, 0) AS AveragePrice
FROM Sales;

3. Data Integrity & Constraint Errors

Error	Meaning	Why It Happens	First Check	Solution
515	Cannot insert NULL	NOT NULL column receives NULL	Column definition and input	Supply a valid value
547	Constraint conflict	FOREIGN KEY/CHECK constraint violated	Related rows and constraint	Correct data or application logic
2601	Cannot insert duplicate key row	Unique index violation	Existing duplicate value	Correct duplicate data or INSERT logic
2627	Violation of PRIMARY KEY/UNIQUE constraint	Duplicate key value	Existing key	Correct INSERT/UPDATE logic
544	Explicit value must be specified for identity column when IDENTITY_INSERT is ON	Identity configuration issue	IDENTITY_INSERT	Correct identity handling
1776	Referenced table has no primary/unique key suitable for FK	Invalid FK definition	Parent table	Reference an appropriate key
1785	Adding FK may create multiple cascade paths	Cascade relationship conflict	FK definitions	Redesign cascade behavior
1788	Foreign key columns don’t match referenced columns	FK definition mismatch	Column types/count	Make FK and referenced columns compatible
3726	Cannot drop object because it is referenced	Dependencies exist	Foreign keys/dependencies	Remove or change dependencies
3728	Constraint cannot be dropped	Dependency or incorrect constraint name	Constraint definition	Verify dependency and name

4. String & Data Truncation Errors

Error	Meaning	Why It Happens	First Check	Solution
8152	String or binary data would be truncated	Source value is larger than destination	Column lengths	Increase destination size or correct source
2628	String or binary data would be truncated with more detail	Value exceeds destination column capacity	Error message/column	Fix source or target column size

Example

CREATE TABLE Employee
(
    Name VARCHAR(10)
);

INSERT INTO Employee
VALUES ('Vivek Johari');

The destination column cannot hold the supplied value.

The correct solution isn’t always “increase the column size.” First determine whether the source data is actually valid.

5. Authentication & Login Errors

Error	Meaning	Why It Happens	First Check	Solution
18456	Login failed	Authentication/login problem	Error state	Check login, password, authentication mode and state
18452	Login failed because login is from an untrusted domain	Windows/domain trust issue	Domain connectivity	Check domain trust and authentication
18461	Login failed because server is in single-user mode	Another connection consumed the available slot	Existing sessions	Identify the connection using the slot
18470	Login failed because login is disabled	Login is disabled	sys.server_principals	Enable login if appropriate
18487	Password expired	Password policy expired login password	Login policy	Reset password
18488	Password must be changed	Login requires password change	Login policy	Change password
17806	SSPI-related authentication error	Kerberos/Windows authentication issue	SPN/domain configuration	Check SPN, service account and Kerberos configuration

Important: Error 18456

Do not stop at:

Login failed for user.

The state value is important for determining the reason.

6. Database Access & Permission Errors

Error	Meaning	Why It Happens	First Check	Solution
229	Permission denied	User lacks required permission	User/role/object permissions	Grant least-privilege permission
262	Permission problem	Required permission isn’t available	Security configuration	Review roles/GRANTs
4060	Cannot open requested database	Login cannot access database or database unavailable	User mapping/database state	Fix mapping or database availability
15151	Cannot alter/drop object	Permission/object ownership issue	User permissions	Correct permissions/ownership
15023	User already exists	Database user already exists	Database principals	Map/fix existing user
15401	Windows account lookup failed	Domain/account issue	Windows/domain	Verify account and domain
15405	Cannot use special principal	Restricted system/security principal	Principal name/type	Review security configuration

7. Transactions, Blocking & Locking

These errors are especially important for DBAs.

Error	Meaning	Why It Happens	First Check	Solution
1204	SQL Server cannot obtain a LOCK resource	Excessive locking/resource pressure	Locks and active transactions	Investigate transaction size/blocking
1205	Transaction chosen as deadlock victim	Two or more transactions are deadlocked	Deadlock graph	Fix access order, indexing or transaction design
1222	Lock request timeout period exceeded	Required lock wasn’t acquired within timeout	Blocking chain	Identify blocker and investigate
1223	Lock request timed out	Lock unavailable	Blocking sessions	Investigate blocking
1224	Lock escalation/resource condition	SQL Server is unable to manage locks as expected	Locking workload	Investigate transactions and lock escalation
1206	Transaction involved in deadlock processing	Transaction deadlock condition	Deadlock information	Analyze deadlock pattern

Error 1205: Deadlock

A common mistake is to simply kill a blocking session.

A deadlock is different from ordinary blocking.

A better approach is:

Capture deadlock → Identify participating queries → Identify resources → Compare access order → Fix root cause

8. Memory & Resource Errors

Error	Meaning	Why It Happens	First Check	Solution
701	Insufficient system memory	SQL Server cannot obtain required memory	SQL/OS memory	Investigate memory pressure
802	Insufficient buffer pool memory	Buffer pool cannot provide required memory	Memory pressure	Investigate workload/configuration
8645	Timeout waiting for memory resources	Query couldn’t obtain execution memory in time	Memory grants	Tune query/workload
8651	Requested memory grant unavailable	Required memory grant isn’t available	Memory grants/resource pool	Reduce query memory requirement or address pressure
8642	Cannot start required thread resources	Parallel query cannot obtain required workers	Parallelism/load	Reduce load or review MAXDOP
8646	Unable to find index entry	Possible index corruption or update-plan problem	Affected index/table	Run DBCC CHECKDB/CHECKTABLE and investigate
8648	Row too large for hash table page	Hash operation encountered row-size limitation	Execution plan/query	Review query; consider appropriate plan strategy
8649	Query cost exceeds configured threshold	Query estimated cost exceeded configured threshold	Query cost/configuration	Review query and relevant threshold/configuration
8653	Query plan cannot be produced because filegroup is offline	Referenced object resides in offline filegroup	Filegroup state	Bring filegroup online if appropriate
8655	Query plan cannot be produced because index is disabled	Query references disabled index	Index status	Rebuild/re-enable or change query/index strategy

Important correction: Error 8646 is not a generic memory error, and 8649 is not a generic parallelism error. Their exact meanings are different and should not be mixed with memory/resource errors.

9. Storage, Disk & Database File Errors

Error	Meaning	Why It Happens	First Check	Solution
1101	Filegroup has insufficient space	Filegroup cannot allocate more space	Database files/free space	Add space or manage files
1105	Could not allocate space	Database/filegroup lacks available space	File size and disk	Increase capacity
1117	Cannot extend file	File growth cannot occur	File growth/disk	Check growth settings and disk
112	Insufficient disk space	Operating system cannot allocate space	Disk	Free/add storage
823	Physical I/O error	Storage/OS I/O failure	SQL Error Log + OS	Investigate storage immediately
824	Logical consistency I/O error	Data read failed a consistency check	Error Log/DBCC	Investigate possible corruption
825	I/O operation required retry	Storage temporarily failed an I/O operation	Error Log/storage	Investigate proactively
945	Database cannot be opened	Database/files aren’t accessible or database state prevents opening	Database state/files	Investigate files and database state
926	Database in recovery state	Database recovery is in progress/problematic	Error Log	Determine recovery status
927	Database is recovering/restoring	Database isn’t ready for normal access	Database state	Wait for operation or investigate
942	Database is offline	Database has been taken offline	Database state	Determine why it is offline
5120	Unable to open database file	File inaccessible	Path and file permissions	Correct permissions/path

Errors 823, 824 and 825

These deserve special attention.

823 generally points toward a physical I/O problem.

824 indicates SQL Server detected a logical consistency problem while processing I/O.

825 means SQL Server had to retry an I/O operation.

Don’t treat these as ordinary application errors. Investigate the SQL Server Error Log, Windows/system logs, storage subsystem and database consistency.

10. Transaction Log Errors

Error	Meaning	Why It Happens	First Check	Solution
9002	Transaction log is full	Log cannot reuse space	log_reuse_wait_desc	Resolve the actual reuse blocker
9003	Invalid log scan number	Log/metadata issue	Error Log	Investigate database/log integrity
3313	Error during database recovery	Recovery encountered a problem	Error Log	Investigate underlying error
3314	Recovery cannot undo operation	Recovery encountered an operation failure	Error Log	Investigate storage/database condition

Don’t blindly increase the log

For Error 9002, first run:

SELECT
    name,
    recovery_model_desc,
    log_reuse_wait_desc
FROM sys.databases;

The important question is:

Why can’t SQL Server reuse the transaction log?

Possible causes include:

• Long-running transaction
• Missing log backups
• Availability Group/replication-related conditions
• Other log-reuse dependencies

11. Backup & Restore Errors

Error	Meaning	Why It Happens	First Check	Solution
3154	Backup belongs to a different database	Backup/database mismatch	Backup metadata	Verify source and target
3156	File cannot be restored	Restore path/file conflict	RESTORE output	Use correct file mapping
3241	Backup media is invalid	Backup may be damaged/incompatible	Backup file/media	Validate backup
3242	Backup media/device problem	Backup media can’t be processed	Storage/media	Check backup file/device
3254	Backup device/file problem	Backup destination issue	Path/permissions/storage	Correct destination
4305	Backup in the log chain is too early	Wrong backup sequence	Backup history	Restore correct sequence
4306	Log backup cannot be applied	LSN/backup chain problem	Backup history	Identify missing/incorrect backup
4326	Log backup contains incomplete recovery information	Backup chain/recovery issue	Backup metadata	Verify backup sequence
4330	Restore operation failed	Restore encountered an error	Full RESTORE output	Investigate underlying error

Best practice: Never troubleshoot a restore error using only the final line of the message. Read the complete RESTORE output.

12. Database State & File Problems

Error	Meaning	Why It Happens	First Check	Solution
5171	Invalid database/file header condition	Database file metadata/header problem	Error Log	Investigate file integrity
5172	Invalid file header	Database file header is invalid	Database files	Investigate possible corruption
5173	File/database association problem	File belongs to another database or metadata mismatch	File metadata	Investigate database files
1823	Cannot create database	Creation/path/resource problem	Disk/path/permissions	Correct creation environment
3729	Cannot drop database	Database is being used	Active sessions	Identify and handle connections
3702	Database currently in use	Active connection exists	Sessions	Disconnect appropriate sessions

13. Connectivity & Network Errors

Some connection errors originate from the client/network stack rather than the SQL Server Database Engine itself, so always investigate the full message.

Error	Meaning	Why It Happens	First Check	Solution
2	File/path not found	Client or SQL operation cannot find specified path	Path	Verify path
5	Access denied / connection-related OS error	Permissions/firewall/resource issue depending on context	Complete message	Check permissions/network
26	Error locating server/instance	Client can’t locate SQL Server	Server/instance name	Verify connection configuration
40	Unable to open connection to SQL Server	Connectivity problem	Server/network	Check SQL service, TCP/IP and firewall
53	Network path/server unavailable	Server cannot be reached	Connectivity	Check DNS/network/firewall
64	Network name unavailable	Connection lost	Network	Investigate network path
10053	Transport-level connection aborted	Host/network software terminated connection	Network/client logs	Investigate network
10054	Connection forcibly closed	Connection reset by peer/network	Network/server	Investigate network and server
10060	Connection timeout	Server didn’t respond in time	Network/firewall	Check connectivity and timeout
17830	Network error during connection	Network/client issue	Network configuration	Investigate connection path

14. Linked Server & Distributed Query Errors

Error	Meaning	Why It Happens	First Check	Solution
7303	Cannot initialize data source	OLE DB/linked-server provider issue	Provider configuration	Test provider and remote connection
7391	Distributed transaction could not start	MSDTC/distributed transaction problem	MSDTC configuration	Check MSDTC or redesign transaction
7399	OLE DB provider reported an error	Remote provider returned an error	Complete provider message	Investigate provider/remote server
7411	Server not configured for RPC	RPC disabled	Linked-server options	Configure RPC if required
7412	Distributed query problem	Remote/linked-server issue	Linked server connection	Test remote server/provider

15. Stored Procedure & Parameter Errors

Error	Meaning	Why It Happens	First Check	Solution
201	Required parameter not supplied	Procedure parameter is missing	Procedure definition	Supply parameter
8144	Too many parameters	Extra parameters supplied	EXEC statement	Remove extra parameters
8145	Parameter already declared	Duplicate parameter	Procedure/call	Remove duplicate
8146	Procedure has no parameters	Parameters supplied to parameterless procedure	EXEC	Remove parameters
2812	Procedure not found	Wrong procedure/database/schema	Object name	Verify procedure

16. Query Processor & Execution Plan Errors

Error	Meaning	First Check	Next Step
8621	Query processor ran out of internal resources	Query complexity	Simplify/rewrite query
8622	Query processor cannot produce plan due to hints/restrictions	Query hints	Remove inappropriate hints
8623	Query processor ran out of internal resources	Complex query	Break query into simpler operations
8630	Internal query processor error	Error log/SQL version	Investigate and check updates
8642	Parallel query cannot obtain required thread resources	CPU/workload/parallelism	Investigate workload and MAXDOP
8645	Timeout waiting for memory resources	Memory grants	Tune query/workload
8646	Index entry cannot be found; possible corruption/update-plan issue	Index/table	Run consistency checks
8648	Hash-table row too large	Execution plan/query	Review query/plan
8649	Estimated query cost exceeds configured threshold	Query cost/configuration	Investigate query and threshold
8651	Requested memory grant unavailable	Memory grant/resource pool	Reduce memory demand/address pressure
8653	Filegroup offline prevents plan generation	Filegroup state	Check filegroup
8655	Disabled index prevents plan generation	Index status	Review/re-enable/rebuild index

Microsoft’s current error catalog confirms these distinctions; for example, 8646 is an index/corruption or update-plan message, 8649 concerns the configured query-cost threshold, 8645 concerns waiting for memory, and 8651 concerns an unavailable memory grant.

17. SQL Server Agent & Job Troubleshooting

SQL Server Agent job failures don’t always have one universal Database Engine error number.

When a SQL Agent job fails, check:

1. Job history
2. Step history
3. SQL Agent error log
4. SQL Server Error Log
5. Job owner
6. Proxy credentials
7. Database permissions
8. CmdExec/PowerShell subsystem
9. Network/share access
10. The actual error returned by the job step

Common problems

Problem	Typical Cause	First Check
Job cannot access database	Permission/login	Job owner/proxy
Job cannot access network share	SQL Agent service account	Share + NTFS permissions
SSIS step fails	Package/environment issue	SSIS execution log
PowerShell step fails	Execution policy/account	Agent subsystem
Job doesn’t start	Schedule/Agent service	SQL Server Agent status

Important: Don’t create artificial error-code mappings for SQL Agent problems. The actual job-step error should be captured and diagnosed.

18. Azure SQL Database Errors

Azure SQL introduces additional transient and resource-governance errors. These should be treated separately from traditional SQL Server errors.

Error	Meaning	Why It Happens	First Check	Solution / Next Step
40197	Service error while processing request	Azure SQL service/infrastructure transient condition	Azure service health + complete message	Retry; investigate if persistent
40501	Service currently busy	Resource governance/throttling	Resource utilization	Retry with backoff and tune workload
40531	Cannot connect/login to server	Azure SQL connectivity/authentication condition	Complete message/network	Check connectivity/authentication
40544	Database reached size quota	Database exceeded configured size limit	Database size	Delete/archive data, optimize storage or scale
40553	Session terminated due to excessive memory usage	Query/session consumed excessive memory	Query/workload	Reduce rows/memory requirement and optimize
40613	Database isn’t currently available	Transient service/database availability condition	Azure status/database state	Retry and investigate if persistent
10928	Resource limit reached	Database/pool worker/session limit reached	Resource ID + workload	Investigate workers/sessions/blocking and scale if appropriate
10929	Server too busy to support requests above current resource guarantee	Resource governance	Resource usage	Retry/tune/scale
49918	Not enough resources to process request	Azure resource pressure	Resource utilization	Retry and investigate workload
49919	Too many create/update operations	Azure management operation limit	Current operations	Wait and retry
49920	Too many operations in progress	Azure resource operation limit	Current operations	Wait and retry
40615	Cannot connect to server	Azure SQL firewall/connectivity issue	Firewall/network	Correct firewall/network configuration

Microsoft specifically identifies 40197, 40613 and related errors as transient conditions, and recommends resilient retry logic for cloud-connected applications. Microsoft also documents 10928/10929 as Azure SQL resource-governance errors and 40501 as an engine-throttling/resource-limit error.

Azure SQL retry principle

For transient errors, don’t simply retry in a tight loop.

Use:

Retry → Delay → Exponential backoff → Maximum retry count → Fail gracefully

Microsoft recommends retry logic for cloud-connected applications and notes that an initial delay of around five seconds can be appropriate for these Azure SQL transient conditions.

19. Security & Permission Troubleshooting Checklist

When you see a permission error, don’t immediately grant db_owner.

Check:

SELECT
    dp.name,
    dp.type_desc,
    dp.authentication_type_desc
FROM sys.database_principals AS dp
WHERE dp.name = USER_NAME();

Then determine:

• Is the login mapped to the correct database user?
• Is the user a member of the appropriate role?
• Does the user have permission on the object?
• Is the object owned by the expected schema?
• Is the application using the expected login?

Use least privilege rather than solving every permission problem with excessive access.

20. The Most Important DBA Error Codes to Remember

If you don’t want to memorize 100+ numbers, start with these:

Error	Remember It As
1205	Deadlock
1222	Lock timeout
1204	Lock resource problem
9002	Transaction log full
1105	Could not allocate database space
823	Physical I/O
824	Logical I/O consistency
825	I/O retry
701	Memory
8645	Memory-resource timeout
8651	Memory grant unavailable
18456	Login failed
4060	Cannot open database
229	Permission denied
208	Invalid object
207	Invalid column
547	Constraint conflict
2601	Duplicate unique index
2627	Duplicate PK/unique constraint
515	NULL into NOT NULL
8152	Data truncation
2628	Detailed truncation
245	Conversion failed
8114	Conversion error
8115	Arithmetic overflow
8134	Divide by zero
40501	Azure SQL service busy
40613	Azure SQL database unavailable
10928	Azure SQL resource limit
10929	Azure SQL resource pressure
40544	Azure SQL database size quota

How to Troubleshoot Any Unknown SQL Server Error

You don’t need to memorize every error number.

Use this process.

              ERROR OCCURS
                   |
                   v
       Capture COMPLETE message
                   |
                   v
       Record error number + state
                   |
                   v
       Identify database/object/session
                   |
                   v
        Check SQL Server Error Log
                   |
                   v
       Check relevant DMV / Query Store
                   |
                   v
       Identify probable root cause
                   |
                   v
           Test the solution
                   |
                   v
        Apply controlled change
                   |
                   v
              Monitor

Useful T-SQL for Error Investigation

1. Find the SQL Server Error Message

SQL Server stores system and user-defined messages in sys.messages. Microsoft documents message_id, severity, event logging status, language and message text in this catalog view.

SELECT message_id, severity, is_event_logged, [text] FROM sys.messages WHERE language_id = 1033 AND message_id = 1205;

Change 1205 to the error number you want to investigate.

2. Search for an Error Number

SELECT
    message_id,
    severity,
    [text]
FROM sys.messages
WHERE language_id = 1033
  AND message_id IN
  (
      1205,
      1222,
      9002,
      823,
      824,
      825,
      18456
  );

3. Check Database State

SELECT
    name,
    state_desc,
    recovery_model_desc,
    user_access_desc
FROM sys.databases;

4. Check Transaction Log Reuse

SELECT
    name,
    recovery_model_desc,
    log_reuse_wait_desc
FROM sys.databases;

This is especially useful for Error 9002.

5. Check Blocking

SELECT
    session_id,
    blocking_session_id,
    wait_type,
    wait_time,
    wait_resource,
    status,
    command
FROM sys.dm_exec_requests
WHERE blocking_session_id <> 0;

Useful for investigating 1222 and general blocking.

6. Check Active Requests

SELECT
    session_id,
    status,
    command,
    cpu_time,
    total_elapsed_time,
    logical_reads,
    reads,
    writes
FROM sys.dm_exec_requests;

7. Capture Errors in TRY…CATCH

For application and stored-procedure troubleshooting:

BEGIN TRY

    -- Your SQL code here

END TRY
BEGIN CATCH

    SELECT
        ERROR_NUMBER() AS ErrorNumber,
        ERROR_SEVERITY() AS ErrorSeverity,
        ERROR_STATE() AS ErrorState,
        ERROR_PROCEDURE() AS ErrorProcedure,
        ERROR_LINE() AS ErrorLine,
        ERROR_MESSAGE() AS ErrorMessage;

END CATCH;

This is especially useful because SQL Server provides functions such as ERROR_NUMBER(), ERROR_SEVERITY(), ERROR_STATE(), ERROR_PROCEDURE(), ERROR_LINE() and ERROR_MESSAGE() for error handling.

Error Code vs Error State

One of the most important concepts for SQL Server troubleshooting is that the error number isn’t always enough.

For example:

Error Number: 18456
State:       XX
Message:     Login failed for user...

The state can provide additional diagnostic information.

Therefore, whenever possible capture:

Error Number
Error Message
Severity
State
Database
Server
Login/User
Procedure
Line Number
Timestamp
Session ID

Don’t Just Search the Error Number

Suppose you see:

SQL Server Error 9002

A beginner might search:

“How to fix SQL Server error 9002?”

and immediately increase the transaction log.

An experienced DBA asks:

“Why is the log not reusable?”

Then checks:

SELECT
    name,
    log_reuse_wait_desc
FROM sys.databases;

Similarly:

Error 1205

Don’t simply kill sessions.

Ask:

Why are these transactions deadlocking?

Error 824

Don’t simply rerun the query.

Ask:

Is there a database/storage consistency problem?

Error 18456

Don’t automatically reset the password.

Ask:

What is the error state and authentication context?

Error 10928

Don’t immediately scale the database.

Ask:

Which resource limit was reached and why?

This difference between error recognition and root-cause analysis is one of the most important skills for a DBA.

SQL Server Error Troubleshooting Cheat Sheet

Error Category	First Tool/Check
Login failure	Error state + SQL Error Log
Permission	Users, roles and permissions
Invalid object	Database/schema/object
Duplicate key	Existing data + index/constraint
FK violation	Parent/child relationship
Blocking	sys.dm_exec_requests
Deadlock	Deadlock graph / Extended Events
Log full	log_reuse_wait_desc
Disk full	Database files + OS storage
I/O error	SQL Error Log + storage
Corruption suspicion	DBCC CHECKDB
Memory issue	Memory grants + resource pressure
Slow query	Query Store + execution plan
Backup failure	Full backup/restore output
Azure throttling	Azure resource metrics
Azure transient error	Retry logic + service health
Network failure	TCP/IP, DNS, firewall and connectivity

DBA Emergency Errors

If you are a SQL Server DBA, take these errors particularly seriously:

823

Possible physical I/O/storage problem.

824

Logical consistency error and possible corruption.

825

Storage/I/O retry warning.

9002

Transaction log is full.

701

Serious memory pressure.

8646

Potential index corruption/update-plan issue.

1205

Deadlock.

1204

Lock resource exhaustion.

The correct response to these errors depends on the environment, but they should not simply be dismissed as ordinary application errors.

SQL Server Error Codes: A Practical Learning Strategy for Freshers

If you’re new to SQL Server, don’t try to memorize all 100+ errors.

Start with these groups:

Beginner

Learn:

102, 105, 207, 208, 245, 515, 547, 8134, 18456, 229

SQL Developer

Add:

2601, 2627, 8152, 2628, 8114, 8115, 8120, 2812

DBA

Add:

1204, 1205, 1222, 9002, 1105, 823, 824, 825, 701, 8645

Azure SQL Professional

Add:

40501, 40613, 10928, 10929, 40544, 40553, 49918, 49919, 49920

This gives you a practical progression rather than trying to memorize a giant list.

Summary

SQL Server has a huge number of system messages, and Microsoft maintains them through the Database Engine error catalog and sys.messages. The catalog is the authoritative place to inspect the actual message, severity and logging characteristics for an installed SQL Server version.

But knowing an error number isn’t enough to become a good SQL Server professional.

The real skill is:

Recognize the error → collect evidence → identify the root cause → choose the safest solution → validate the result.

You don’t need to Google or ask AI every time a familiar error appears.

Use this cheat sheet as your first reference, then use Microsoft’s documentation, SQL Server logs, DMVs, Query Store, execution plans, Extended Events and other diagnostic tools when deeper investigation is required.

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SQL Server & DBA Error Codes Cheat Sheet – 100+ Common Errors, Causes & Solutions

Keep it handy whenever you’re working with SQL Server.

Official Microsoft reference: Microsoft’s Database Engine error catalog and sys.messages should be used to verify error details for the specific SQL Server version/environment you’re troubleshooting.