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SQL 教程

SQL 主页 SQL 简介 SQL 语法 SQL 选择 SQL 选择 DISTINCT SQL WHERE SQL ORDER BY SQL AND SQL OR SQL NOT SQL 插入 SQL 空值 SQL 更新 SQL 删除 SQL 选择 TOP SQL 聚合函数 SQL 最小值和最大值 SQL 计数 SQL 求和 SQL 平均值 SQL LIKE SQL 通配符 SQL IN SQL BETWEEN SQL 别名 SQL 连接 SQL 内连接 SQL 左连接 SQL 右连接 SQL 全连接 SQL 自连接 SQL 并集 SQL 分组 SQL HAVING SQL EXISTS SQL ANY, ALL SQL SELECT INTO SQL INSERT INTO SELECT SQL CASE SQL 空值函数 SQL 存储过程 SQL 注释 SQL 运算符

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SQL 关键字
ADD ADD CONSTRAINT ALL ALTER ALTER COLUMN ALTER TABLE AND ANY AS ASC BACKUP DATABASE BETWEEN CASE CHECK COLUMN CONSTRAINT CREATE CREATE DATABASE CREATE INDEX CREATE OR REPLACE VIEW CREATE TABLE CREATE PROCEDURE CREATE UNIQUE INDEX CREATE VIEW DATABASE DEFAULT DELETE DESC DISTINCT DROP DROP COLUMN DROP CONSTRAINT DROP DATABASE DROP DEFAULT DROP INDEX DROP TABLE DROP VIEW EXEC EXISTS FOREIGN KEY FROM FULL OUTER JOIN GROUP BY HAVING IN INDEX INNER JOIN INSERT INTO INSERT INTO SELECT IS NULL IS NOT NULL JOIN LEFT JOIN LIKE LIMIT NOT NOT NULL OR ORDER BY OUTER JOIN PRIMARY KEY PROCEDURE RIGHT JOIN ROWNUM SELECT SELECT DISTINCT SELECT INTO SELECT TOP SET TABLE TOP TRUNCATE TABLE UNION UNION ALL UNIQUE UPDATE VALUES VIEW WHERE
MySQL 函数
字符串函数: ASCII CHAR_LENGTH CHARACTER_LENGTH CONCAT CONCAT_WS FIELD FIND_IN_SET FORMAT INSERT INSTR LCASE LEFT LENGTH LOCATE LOWER LPAD LTRIM MID POSITION REPEAT REPLACE REVERSE RIGHT RPAD RTRIM SPACE STRCMP SUBSTR SUBSTRING SUBSTRING_INDEX TRIM UCASE UPPER 数值函数: ABS ACOS ASIN ATAN ATAN2 AVG CEIL CEILING COS COT COUNT DEGREES DIV EXP FLOOR GREATEST LEAST LN LOG LOG10 LOG2 MAX MIN MOD PI POW POWER RADIANS RAND ROUND SIGN SIN SQRT SUM TAN TRUNCATE 日期函数: ADDDATE ADDTIME CURDATE CURRENT_DATE CURRENT_TIME CURRENT_TIMESTAMP CURTIME DATE DATEDIFF DATE_ADD DATE_FORMAT DATE_SUB DAY DAYNAME DAYOFMONTH DAYOFWEEK DAYOFYEAR EXTRACT FROM_DAYS HOUR LAST_DAY LOCALTIME LOCALTIMESTAMP MAKEDATE MAKETIME MICROSECOND MINUTE MONTH MONTHNAME NOW PERIOD_ADD PERIOD_DIFF QUARTER SECOND SEC_TO_TIME STR_TO_DATE SUBDATE SUBTIME SYSDATE TIME TIME_FORMAT TIME_TO_SEC TIMEDIFF TIMESTAMP TO_DAYS WEEK WEEKDAY WEEKOFYEAR YEAR YEARWEEK 高级函数: BIN BINARY CASE CAST COALESCE CONNECTION_ID CONV CONVERT CURRENT_USER DATABASE IF IFNULL ISNULL LAST_INSERT_ID NULLIF SESSION_USER SYSTEM_USER USER VERSION
SQL Server 函数
字符串函数: ASCII CHAR CHARINDEX CONCAT 使用 + 连接 CONCAT_WS DATALENGTH DIFFERENCE FORMAT LEFT LEN LOWER LTRIM NCHAR PATINDEX QUOTENAME REPLACE REPLICATE REVERSE RIGHT RTRIM SOUNDEX SPACE STR STUFF SUBSTRING TRANSLATE TRIM UNICODE UPPER 数值函数: ABS ACOS ASIN ATAN ATN2 AVG CEILING COUNT COS COT DEGREES EXP FLOOR LOG LOG10 MAX MIN PI POWER RADIANS RAND ROUND SIGN SIN SQRT SQUARE SUM TAN 日期函数: CURRENT_TIMESTAMP DATEADD DATEDIFF DATEFROMPARTS DATENAME DATEPART DAY GETDATE GETUTCDATE ISDATE MONTH SYSDATETIME YEAR 高级函数 CAST COALESCE CONVERT CURRENT_USER IIF ISNULL ISNUMERIC NULLIF SESSION_USER SESSIONPROPERTY SYSTEM_USER USER_NAME
MS Access 函数
字符串函数: Asc Chr 使用 & 连接 CurDir Format InStr InstrRev LCase Left Len LTrim Mid Replace Right RTrim Space Split Str StrComp StrConv StrReverse Trim UCase 数值函数: Abs Atn Avg Cos Count Exp Fix Format Int Max Min Randomize Rnd Round Sgn Sqr Sum Val 日期函数: Date DateAdd DateDiff DatePart DateSerial DateValue Day Format Hour Minute Month MonthName Now Second Time TimeSerial TimeValue Weekday WeekdayName Year 其他函数: CurrentUser Environ IsDate IsNull IsNumeric
SQL 快速参考

SQL 示例

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SQL Server NULLIF() 函数

❮ 上一篇 ❮ SQL Server 函数 下一篇 ❯

示例

比较两个表达式

SELECT NULLIF(25, 25);
自己试试 »

定义和用法

如果两个表达式相等，NULLIF() 函数返回 NULL，否则返回第一个表达式。

语法

NULLIF(expr1, expr2)

参数值

参数 描述
expr1, expr2 必需。要比较的两个表达式

技术细节

适用于 SQL Server（从 2008 开始）、Azure SQL 数据库、Azure SQL 数据仓库、并行数据仓库

更多示例

示例

比较两个表达式

SELECT NULLIF('Hello', 'Hello');
自己试试 »

示例

比较两个表达式

SELECT NULLIF('Hello', 'world');
自己试试 »

示例

比较两个表达式

SELECT NULLIF('2017-08-25', '2017-08-25');
自己试试 »

❮ 上一篇 ❮ SQL Server 函数 下一篇 ❯
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