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When migrating databases from MS SQL to MySQL server it is often necessary to translate MS SQL queries according to MySQL syntax as well. Syntax of SQL queries in MS SQL and MySQL are similar but not identical. This article discovers 10 most popular differences between MS SQL and MySQL syntax. 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`.

   Also, MS 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.

2. SQL Server uses function CHARINDEX to search substring into string. MySQL equivalent for this function is LOCATE.
3. CONVERT() function is used to convert an expression of one data type to another in MS 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. See special note on using CONVERT() for DATETIME values.
4. MS SQL function IIF($boolean_expression, $true_value, $false_value) that returns $true_value or $false_value value depending on $boolean_expression, must be replaced by IF in MySQL.
5. LEN() function returns length of string expression in MS SQL. MySQL equivalent for this function is LENGTH().
6. MS SQL function DATEADD adds interval to the specified part of the date. MySQL operator '+' can do the same as follows:

   DATEADD(year,  1, $date$) -> $date$ + interval 1 year
   DATEADD(month, 1, $date$) -> $date$ + interval 1 month
   DATEADD(day,   1, $date$) -> $date$ + interval 1 day
   

   where $date$ is an expression of DATE type. Function DATEDIFF($datepart, $startdate, $enddate) returns $datepart part of substructing $startdate from $enddate. It can be converted into MySQL as follows:

   DATEDIFF(hour, $startdate, $enddate)   -> TIMESTAMPDIFF(hour, $enddate, $startdate)
   DATEDIFF(minute, $startdate, $enddate) -> TIMESTAMPDIFF(minute, $enddate, $startdate)
   DATEDIFF(month, $startdate, $enddate)  -> TIMESTAMPDIFF(month, $enddate, $startdate)
   

In general, Microsoft SQL and MySQL have different sets of date processing functions, although most of them can be replicated as follows:

DATENAME(month,   $date$) -> DATE_FORMAT($date$, '%M') or MONTHNAME(expression)
DATENAME(weekday, $date$) -> DATE_FORMAT($date$, '%W') or DAYNAME(expression)
DATEPART(year,    $date$) -> DATE_FORMAT($date$, '%Y')
DATEPART(month,   $date$) -> DATE_FORMAT($date$, '%m')
DATEPART(day,     $date$) -> DATE_FORMAT($date$, '0')
GETDATE()                 -> NOW()
GETUTCDATE()              -> UTC_TIMESTAMP()

where $date$ is an expression of DATE type.

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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