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MySQL 教程

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MySQL 数据类型 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

MySQL 例子

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MySQL ISNULL() 函数

❮ MySQL 函数

例子

测试表达式是否为 NULL

SELECT ISNULL(NULL);
自己试试 »

定义和用法

ISNULL() 函数根据表达式是否为 NULL 返回 1 或 0。

如果表达式为 NULL，该函数返回 1。否则，它返回 0。

语法

ISNULL(expression)

参数值

参数 描述
expression 必需。要测试的值

技术细节

工作于 从 MySQL 4.0 开始

更多例子

例子

测试表达式是否为 NULL

SELECT ISNULL("");
自己试试 »

例子

测试表达式是否为 NULL

SELECT ISNULL(350);
自己试试 »

例子

测试表达式是否为 NULL

SELECT ISNULL("Hello world!");
自己试试 »

❮ MySQL 函数

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