Difference between revisions of "Microsoft SQL Server"
(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
Contents
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.
