MSSQL与PLSQL的区别

更多请参考： http://www.bristle.com/Tips/SQL.htm#Oracle%20Tips

黄色背景为经常用并且容易用错的条目

语法结构

Description	Oracle	MS SQL Server
Left Outer Join	WHERE column1 = column2(+)	FROM table1 LEFT OUTER JOIN table2 ON table1.column1 = table2.column2 Note:  The following syntax is also supported, but is no longer recommended: WHERE column1 *= column2
Right Outer Join	WHERE column1(+) = column2	FROM table1 RIGHT OUTER JOIN table2 ON table1.column1 = table2.column2 Note:  The following syntax is also supported, but is no longer recommended: WHERE column1 =* column2
SELECT data into a table	CREATE TABLE AS SELECT ...	SELECT ... INTO
Intersection of 2 SELECTS	SELECT ... INTERSECT SELECT ...	SELECT ... WHERE EXISTS (SELECT ...)
INSERT into a JOIN	INSERT INTO SELECT ...	Create a VIEW and INSERT INTO it.
UPDATE data in a JOIN	UPDATE SELECT...	Create a VIEW and INSERT INTO it.
UPDATE one table based on criteria in another table	<not supported>	UPDATE table FROM ...
DELETE rows from one table based on criteria in another table	<not supported>	DELETE FROM table FROM ...
DROP a column from a table	<not supported until Oracle 8i>	ALTER TABLE table_name DROP COLUMN column_name
Readonly VIEW	CREATE VIEW ... WITH READONLY	GRANT SELECT ...
Save point	SAVEPOINT	SAVE TRANSACTION
Declaring a local variable	DECLARE varname type;	DECLARE @varname type
Assigning to a variable	varname := value SELECT value INTO varname	SET @varname = value SELECT @varname = value
Assigning to a variable from a cursor	FETCH cursorname INTO varname	FETCH NEXT FROM cursorname INTO varname
Declaring a cursor	CURSOR curname (params) IS SELECT ...;	DECLARE curname CURSOR FOR SELECT ...
If statement	IF ... THEN ELSIF ... THEN ELSE ENDIF	IF ... BEGIN ... END ELSE BEGIN ... END
While loop	WHILE ... LOOP END LOOP	WHILE ... BEGIN ... END
Other loops	FOR ... END LOOP LOOP ... END LOOP	<not supported>
Loop exit	EXIT, EXIT WHEN	BREAK, CONTINUE

数据类型

Data Type	In VB6	Oracle	MS SQL Server
Fixed Length String	String	CHAR(n) - limit 2KB	CHAR(n), CHARACTER(n) - limit 255 (6.5) - limit 8KB (7.0)
Variable Length String	String	VARCHAR2(n), VARCHAR(n) - limit 4KB in a column - limit 32KB in a variable - VARCHAR is obsolete	VARCHAR(n), CHAR VARYING(n), CHARACTER VARYING(n) - limit 255 (6.5) - limit 8KB (7.0)
Integer	Integer	INTEGER, INTEGER(n), SMALLINT	INTEGER (4 bytes), INT (4 bytes), SMALLINT (2 bytes), TINYINT (1 byte), BIT (1 bit)
Fixed Point	Long/Currency	NUMBER, NUMBER(n), NUMBER(n,d), FLOAT, FLOAT(n), FLOAT(n,d)	NUMERIC, NUMERIC(n), NUMERIC(n,d), DECIMAL, DECIMAL(n), DECIMAL(n,d), DEC, DEC(n), DEC(n,d), MONEY, SMALLMONEY
Floating Point	Currency	DECIMAL	FLOAT, FLOAT(n), DOUBLE PRECISION, REAL,
Date	Date	DATE	DATETIME, SMALLDATETIME, TIMESTAMP - TIMESTAMP auto-updated
Row Identifier	<none>	implicit ROWID column	(use an IDENTITY column)

常用函数

Description	Oracle	MS SQL Server
Modulus	MOD	%
Translate NULL to n	NVL	ISNULL
Return NULL if two values are equal	DECODE	NULLIF
String concatenation	CONCAT(str1,str2)	str1 + str2
Convert ASCII to char	CHR	CHAR
Find string in string	INSTR	CHARINDEX
Find pattern in string	INSTR	PATINDEX
String length	LENGTH	DATALENGTH
Trim leading or trailing chars other than blanks	LTRIM(str,chars), RTRIM(str,chars)	<none>
Replace chars in string	REPLACE	STUFF
Convert number to string	TO_CHAR	STR, CAST
Convert string to number	TO_NUMBER	CAST
Get substring from string	SUBSTR	SUBSTRING
Char for char translation in string	TRANSLATE	<none>
Date addition	ADD_MONTH or +	DATEADD
Convert date to string	TO_CHAR	DATENAME, CONVERT
Convert string to date	TO_DATE	CAST
Convert date to number	TO_NUMBER(TO_CHAR(d))	DATEPART
Date round	ROUND	CONVERT
Date truncate	TRUNC	CONVERT
Current date	SYSDATE	GETDATE
If statement in an expression	DECODE ex)DECODE (expression, search_1,result_1,..., search_n,result_n)	CASE ... WHEN or COALESCE ex)SELECT      CASE expression           WHEN serch_1           THEN result_1           ....           WHEN search_n           THEN  result_n

ORACLE 与SQL SERVER间的转换

 　　如需在Oracle 数据库与Sql Server 数据库之间进行转换需要做好以下工作：

　　1）保证所有的 SELECT, INSERT, UPDATE, and DELETE 语句的语法是正确的，如果有什么不同需要做一定的更改。
2）改变所有ORACLE中的 outer joins 为SQL SERVER支持的 SQL-92 standard outer join 标准。
3）将Oracle functions 与SQL Server functions 进行转换。
4）检查所有的操作符.。
5）将ORACLE的“||” 字串连接操作符转换为SQL SERVER的 “+”字串连接操作符。
6）将ORACLE的 PL/SQL 程序转换为SQL SERVER的TransactSQL 程序。
7）修改所有的ORACLE的 PL/SQL 游标为没有游标的SELECT 语句或者是SQL SERVER的 TransactSQL 游标。
8）将ORACLE的PL/SQL procedures, functions, and packages 与SQL SERVER的TransactSQL procedures进行转换。
9）将ORACLE的 PL/SQL triggers与SQL SERVER的TransactSQL triggers进行转换。
10）用 SET SHOWPLAN 语句来调整你的查询的性能。