The following table specifies the maximum sizes and numbers of various objects defined in SQL Server databases or referenced in Transact-SQL statements.

SQL Server Database Engine object	Maximum sizes/numbers SQL Server (32-bit)	Maximum sizes/numbers SQL Server (64-bit)
Batch size1	65,536 * Network Packet Size	65,536 * Network Packet Size
Bytes per short string column	8,000	8,000
Bytes per GROUP BY, ORDER BY	8,060	8,060
Bytes per index key2	900	900
Bytes per foreign key	900	900
Bytes per primary key	900	900
Bytes per row8	8,060	8,060
Bytes in source text of a stored procedure	Lesser of batch size or 250 MB	Lesser of batch size or 250 MB
Bytes per varchar(max), varbinary(max), xml, text, or image column	2^31-1	2^31-1
Characters per ntext or nvarchar(max) column	2^30-1	2^30-1
Clustered indexes per table	1	1
Columns in GROUP BY, ORDER BY	Limited only by number of bytes	Limited only by number of bytes
Columns or expressions in a GROUP BY WITH CUBE or WITH ROLLUP statement	10	10
Columns per index key7	16	16
Columns per foreign key	16	16
Columns per primary key	16	16
Columns per nonwide table	1,024	1,024
Columns per wide table	30,000	30,000
Columns per SELECT statement	4,096	4,096
Columns per INSERT statement	4096	4096
Connections per client	Maximum value of configured connections	Maximum value of configured connections
Database size	524,272 terabytes	524,272 terabytes
Databases per instance of SQL Server	32,767	32,767
Filegroups per database	32,767	32,767
Files per database	32,767	32,767
File size (data)	16 terabytes	16 terabytes
File size (log)	2 terabytes	2 terabytes
Foreign key table references per table4	253	253
Identifier length (in characters)	128	128
Instances per computer	50 instances on a stand-alone server for all SQL Server editions except for Workgroup. Workgroup supports a maximum of 16 instances per computer. SQL Server supports 25 instances on a failover cluster.	50 instances on a stand-alone server. 25 instances on a failover cluster.
Length of a string containing SQL statements (batch size)1	65,536 * Network packet size	65,536 * Network packet size
Locks per connection	Maximum locks per server	Maximum locks per server
Locks per instance of SQL Server5	Up to 2,147,483,647	Limited only by memory
Nested stored procedure levels6	32	32
Nested subqueries	32	32
Nested trigger levels	32	32
Nonclustered indexes per table	999	999
Number of distinct expressions in the GROUP BY clause when any of the following are present: CUBE, ROLLUP, GROUPING SETS, WITH CUBE, WITH ROLLUP	32	32
Number of grouping sets generated by operators in the GROUP BY clause	4,096	4,096
Parameters per stored procedure	2,100	2,100
Parameters per user-defined function	2,100	2,100
REFERENCES per table	253	253
Rows per table	Limited by available storage	Limited by available storage
Tables per database3	Limited by number of objects in a database	Limited by number of objects in a database
Partitions per partitioned table or index	1,000	1,000
Statistics on non-indexed columns	30,000	30,000
Tables per SELECT statement	256	256
Triggers per table3	Limited by number of objects in a database	Limited by number of objects in a database
Columns per UPDATE statement (Wide Tables)	4096	4096
User connections	32,767	32,767
XML indexes	249	249

¹Network Packet Size is the size of the tabular data stream (TDS) packets used to communicate between applications and the relational Database Engine. The default packet size is 4 KB, and is controlled by the network packet size configuration option.

²The maximum number of bytes in any index key cannot exceed 900 in SQL Server. You can define a key using variable-length columns whose maximum sizes add up to more than 900, provided no row is ever inserted with more than 900 bytes of data in those columns. In SQL Server, you can include nonkey columns in a nonclustered index to avoid the maximum index key size of 900 bytes.

³Database objects include objects such as tables, views, stored procedures, user-defined functions, triggers, rules, defaults, and constraints. The sum of the number of all objects in a database cannot exceed 2,147,483,647.

⁴Although a table can contain an unlimited number of FOREIGN KEY constraints, the recommended maximum is 253. Depending on the hardware configuration hosting SQL Server, specifying additional FOREIGN KEY constraints may be expensive for the query optimizer to process.

⁵This value is for static lock allocation. Dynamic locks are limited only by memory.

⁶If a stored procedure accesses more than 8 databases, or more than 2 databases in interleaving, you will receive an error.

⁷If the table contains one or more XML indexes, the clustering key of the user table is limited to 15 columns because the XML column is added to the clustering key of the primary XML index. In SQL Server, you can include nonkey columns in a nonclustered index to avoid the limitation of a maximum of 16 key columns. For more information, see Index with Included Columns.

⁸ SQL Server supports row-overflow storage which enables variable length columns to be pushed off-row. Only a 24-byte root is stored in the main record for variable length columns pushed out of row; because of this, the effective row limit is higher than in previous releases of SQL Server. For more information, see the "Row-Overflow Data Exceeding 8 KB" topic in SQL Server Books Online.

The following table specifies the maximum sizes and numbers of various objects defined in SQL Server Replication.

SQL Server Replication object	Maximum sizes/numbers SQL Server (32-bit)	Maximum sizes/numbers SQL Server (64-bit)
Articles (merge publication)	256	256
Articles (snapshot or transactional publication)	32,767	32,767
Columns in a table1 (merge publication)	246	246
Columns in a table2 (SQL Server snapshot or transactional publication)	1,000	1,000
Columns in a table2 (Oracle snapshot or transactional publication)	995	995
Bytes for a column used in a row filter (merge publication)	1,024	1,024
Bytes for a column used in a row filter (snapshot or transactional publication)	8,000	8,000

¹If row tracking is used for conflict detection (the default), the base table can include a maximum of 1,024 columns, but columns must be filtered from the article so that a maximum of 246 columns is published. If column tracking is used, the base table can include a maximum of 246 columns. For more information on the tracking level, see the "Tracking Level" section of How Merge Replication Detects and Resolves Conflicts.

²The base table can include the maximum number of columns allowable in the publication database (1,024 for SQL Server), but columns must be filtered from the article if they exceed the maximum specified for the publication type.

Reference