目录
-
SQL 教程
- SQL 主页
- SQL 简介
- SQL 语法
- SQL Select
- SQL Select Distinct
- SQL Where
- SQL Order By
- SQL And
- SQL Or
- SQL Not
- SQL Insert Into
- SQL Null 值
- SQL Update
- SQL Delete
- SQL Select Top
- SQL Min and Max
- SQL Count
- SQL Sum
- SQL Avg
- SQL Like
- SQL 通配符
- SQL In
- SQL Between
- SQL 别名
- SQL 连接
- SQL Inner Join
- SQL Left Join
- SQL Right Join
- SQL Full Join
- SQL 自连接
- SQL Union
- SQL Group By
- SQL Having
- SQL Exists
- SQL Any, All
- SQL Select Into
- SQL Insert Into Select
- SQL Case
- SQL Null 函数
- SQL 存储过程
- SQL 注释
- SQL 运算符
- SQL 数据库
-
SQL 参考
-
SQL 关键字
- 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
- MySQL 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
- 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
- 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
- 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
- SQL Server 函数
- ASCII
- CHAR
- CHARINDEX
- CONCAT
- Concat with +
- 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
- 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
- CURRENT_TIMESTAMP
- DATEADD
- DATEDIFF
- DATEFROMPARTS
- DATENAME
- DATEPART
- DAY
- GETDATE
- GETUTCDATE
- ISDATE
- MONTH
- SYSDATETIME
- YEAR
- CAST
- COALESCE
- CONVERT
- CURRENT_USER
- IIF
- ISNULL
- ISNUMERIC
- NULLIF
- SESSION_USER
- SESSIONPROPERTY
- SYSTEM_USER
- USER_NAME
-
MS Access 函数
- MS Access 函数
- Asc
- Chr
- Concat with &
- CurDir
- Format
- InStr
- InstrRev
- LCase
- Left
- Len
- LTrim
- Mid
- Replace
- Right
- RTrim
- Space
- Split
- Str
- StrComp
- StrConv
- StrReverse
- Trim
- UCase
- Abs
- Atn
- Avg
- Cos
- Count
- Exp
- Fix
- Format
- Int
- Max
- Min
- Randomize
- Rnd
- Round
- Sgn
- Sqr
- Sum
- Val
- Date
- DateAdd
- DateDiff
- DatePart
- DateSerial
- DateValue
- Day
- Format
- Hour
- Minute
- Month
- MonthName
- Now
- Second
- Time
- TimeSerial
- TimeValue
- Weekday
- WeekdayName
- Year
- CurrentUser
- Environ
- IsDate
- IsNull
- IsNumeric
- SQL 快速参考
-
SQL 关键字
- SQL 示例
SQL DROP COLUMN 关键字
DROP COLUMN
这个DROP COLUMN命令用于删除现有表中的列。
以下 SQL 从 "Customers" 表中删除 "ContactName" 列：
示例
ALTER TABLE Customers
DROP COLUMN ContactName;
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