When migrating databases from Microsoft SQL Server to MySQL, it is often necessary to translate SQL Server queries to the MySQL syntax. The syntax of SQL queries in both database systems are similar but not identical. This article discovers 10 most popular differences between the SQL Server and MySQL syntaxes. The target audience for this guide should have general database management knowledge and experience in composing SQL queries.
1) Sometime MS SQL table or column names are enclosed in square brackets in queries (e.g. if contains spaces or for some other reasons). MySQL does not allow square brackets around table of column names, they all must be replaced by ` symbol or cut off: [object] -> `object`.
2) Microsoft SQL provides effective solution to avoid naming objects conflict and to manage user permissions on data access. This is schema, a logic container used to group and categorize objects inside the single database. When using schema the full name of database object in query may look like %database%.%schema%.%object%. However, there is no such semantic in MySQL, so all schema names must be cut off from queries.
3) CONVERT() function is used to convert an expression of one data type to another in Microsoft SQL. In MySQL CONVERT() function converts text data between different character sets. However, there is equivalent function CAST(), so every occurrence of 'convert(%type%, %expression%)' in MS SQL query must be replaced by 'cast(%expression% AS %type%)' in MySQL query.
4) LEN() function returns length of string expression in MS SQL. MySQL equivalent for this function is LENGTH().
5) Microsoft SQL function DATEADD() adds interval to the specified part of the date. MySQL operator '+' can do the same as follows:
DATEADD(year, 1, %expression%) -> %expression% + interval 1 year
DATEADD(month, 1, %expression%) -> %expression% + interval 1 month
DATEADD(day, 1, %expression%) -> %expression% + interval 1 day
6) GETDATE() function returns the current system date and time in MS SQL. MySQL equivalent for this function is NOW().
7) MS SQL operator '+' allows to concatenate strings like this: 'string1' + 'string2'. In MySQL such expressions must be replaced by CONCAT('string1', 'string2').
8) MS SQL function CONTAINS(expression, template) searches for matches of template inside expression. MySQL has operator LIKE that implements the same semantics: expression LIKE %template%
9) If MS SQL query contains 'TOP (100) PERCENT' pattern just cut it off when composing MySQL query. If there is another percentage amount in that pattern, it can be replace by the following code in MySQL (works in MySQL 5.0.7 and higher):
SET @amount =(SELECT COUNT(*) FROM %table name%) * %percentage% / 10;
PREPARE STMT FROM '%original query% FROM %table name% LIMIT ?';
EXECUTE STMT USING @amount;
10) Syntax of JOIN constructions are very similar in MS SQL and MySQL. The only difference is that MS SQL keyword 'WHERE' is replaced by 'ON' in MySQL. For example:
'... %table1% cross join %table2% where %condition%'
must be translated into
'... %table1% cross join %table2% on %condition%'
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