Difference between revisions of "Microsoft SQL Server"

From Organic Design wiki
(IGNORE)
m
Line 32: Line 32:
 
|}
 
|}
  
== AUTOINCREMENT vs IDENTITY ==
+
== Changes to INSERT wrapper ==
 +
=== AUTOINCREMENT vs IDENTITY ===
 
MySQL style ''AUTOINCREMENT'' columns are inplemented in MSSQL using ''IDENTITY(x,y)'' where ''x'' is the initial value and ''y'' is the amount to add on each insert. The last value resulting from an insert into an IDENTITY column is stored in the ''@@IDENTITY'' variable. These kinds of columns are usually used as primary keys and are therefore assigned the ''NOT NULL'' property.
 
MySQL style ''AUTOINCREMENT'' columns are inplemented in MSSQL using ''IDENTITY(x,y)'' where ''x'' is the initial value and ''y'' is the amount to add on each insert. The last value resulting from an insert into an IDENTITY column is stored in the ''@@IDENTITY'' variable. These kinds of columns are usually used as primary keys and are therefore assigned the ''NOT NULL'' property.
  
Line 38: Line 39:
  
 
To get round this in the MediaWiki MSSQL layer, I've modified the insert wrapper in the ''DatabaseMssql'' class to check if the primary key is used in the insert and remove it if so. It checks this by assuming that the primary key will be of the same name as the table but with ''_id'' on the end, and that it will the first item in the list of columns to update.
 
To get round this in the MediaWiki MSSQL layer, I've modified the insert wrapper in the ''DatabaseMssql'' class to check if the primary key is used in the insert and remove it if so. It checks this by assuming that the primary key will be of the same name as the table but with ''_id'' on the end, and that it will the first item in the list of columns to update.
 +
 +
=== IGNORE ===
 +
As you can see from the comparison table above, the MySQL ''INSERT IGNORE'' option takes quite a different form in MSSQL. This is handled in the ''insert'' wrapper method. In the case of multiple row inserts, a separate conditional insert query is performed for each item.
  
 
== See also ==
 
== See also ==

Revision as of 12:13, 10 May 2008

Syntax differences between MySQL and MSSQL

MySQL MSSQL
AUTO_INCREMENT IDENTITY(1,1)
bool bit
[UN]SIGNED not valid
SELECT * FROM foo LIMIT x SELECT TOP x * FROM foo
SELECT * FROM foo LIMIT x,y not sure how to implement yet
INSERT IGNORE INTO foo (foo_id,bar) VALUES ('1','xyz') IF NOT EXISTS (SELECT * FROM foo WHERE foo_id = '1') INSERT INTO foo (foo_id,bar) VALUES ('1','xyz')
IF(cond,trueVal,falseVal) CASE WHEN cond THEN trueVal ELSE falseVal END
SHOW TABLES SELECT * FROM INFORMATION_SCHEMA.TABLES
ENUM not natively supported, change to text

MSSQL Variables

@@VERSION Server version information
@@IDENTITY Last inserted row
@@ERROR Last error number

Changes to INSERT wrapper

AUTOINCREMENT vs IDENTITY

MySQL style AUTOINCREMENT columns are inplemented in MSSQL using IDENTITY(x,y) where x is the initial value and y is the amount to add on each insert. The last value resulting from an insert into an IDENTITY column is stored in the @@IDENTITY variable. These kinds of columns are usually used as primary keys and are therefore assigned the NOT NULL property.

In MySQL the standard way of inserting data into rows exhibiting AUTOINCREMENT columns is simply to use a NULL value which will be ignored. In MSSQL however assigning a NULL to an IDENTITY column is not allowed, instead the best way is not to include those items in the list of columns to be updated at all.

To get round this in the MediaWiki MSSQL layer, I've modified the insert wrapper in the DatabaseMssql class to check if the primary key is used in the insert and remove it if so. It checks this by assuming that the primary key will be of the same name as the table but with _id on the end, and that it will the first item in the list of columns to update.

IGNORE

As you can see from the comparison table above, the MySQL INSERT IGNORE option takes quite a different form in MSSQL. This is handled in the insert wrapper method. In the case of multiple row inserts, a separate conditional insert query is performed for each item.

See also