Syntax. The syntax to drop a column in a table in MySQL (using the ALTER TABLE statement) is: ALTER TABLE table_name DROP COLUMN column_name; table_name.
DROP TABLE always removes any indexes, rules, triggers, and constraints that exist for the target table. However, to drop a table that is referenced by a view or a foreign-key constraint of another table, CASCADE must be specified.
Right-click the column you want to delete and choose Delete Column from the shortcut menu. If the column participates in a relationship (FOREIGN KEY or PRIMARY KEY), a message prompts you to confirm the deletion of the selected columns and their relationships. Choose Yes.
First you should drop the problematic DEFAULT constraint
, after that you can drop the column
alter table tbloffers drop constraint [ConstraintName]
go
alter table tbloffers drop column checkin
But the error may appear from other reasons - for example the user defined function or view with SCHEMABINDING
option set for them.
UPD: Completely automated dropping of constraints script:
DECLARE @sql NVARCHAR(MAX)
WHILE 1=1
BEGIN
SELECT TOP 1 @sql = N'alter table tbloffers drop constraint ['+dc.NAME+N']'
from sys.default_constraints dc
JOIN sys.columns c
ON c.default_object_id = dc.object_id
WHERE
dc.parent_object_id = OBJECT_ID('tbloffers')
AND c.name = N'checkin'
IF @@ROWCOUNT = 0 BREAK
EXEC (@sql)
END
Here's another way to drop a default constraint with an unknown name without having to first run a separate query to get the constraint name:
DECLARE @ConstraintName nvarchar(200)
SELECT @ConstraintName = Name FROM SYS.DEFAULT_CONSTRAINTS
WHERE PARENT_OBJECT_ID = OBJECT_ID('__TableName__')
AND PARENT_COLUMN_ID = (SELECT column_id FROM sys.columns
WHERE NAME = N'__ColumnName__'
AND object_id = OBJECT_ID(N'__TableName__'))
IF @ConstraintName IS NOT NULL
EXEC('ALTER TABLE __TableName__ DROP CONSTRAINT ' + @ConstraintName)
You can also drop the column and its constraint(s) in a single statement rather than individually.
CREATE TABLE #T
(
Col1 INT CONSTRAINT UQ UNIQUE CONSTRAINT CK CHECK (Col1 > 5),
Col2 INT
)
ALTER TABLE #T DROP CONSTRAINT UQ ,
CONSTRAINT CK,
COLUMN Col1
DROP TABLE #T
(but not other possible column dependencies such as foreign keys, unique and primary key constraints, computed columns, indexes)
CREATE TABLE [dbo].[TestTable]
(
A INT DEFAULT '1' CHECK (A=1),
B INT,
CHECK (A > B)
)
GO
DECLARE @TwoPartTableNameQuoted nvarchar(500) = '[dbo].[TestTable]',
@ColumnNameUnQuoted sysname = 'A',
@DynSQL NVARCHAR(MAX);
SELECT @DynSQL =
'ALTER TABLE ' + @TwoPartTableNameQuoted + ' DROP' +
ISNULL(' CONSTRAINT ' + QUOTENAME(OBJECT_NAME(c.default_object_id)) + ',','') +
ISNULL(check_constraints,'') +
' COLUMN ' + QUOTENAME(@ColumnNameUnQuoted)
FROM sys.columns c
CROSS APPLY (SELECT ' CONSTRAINT ' + QUOTENAME(OBJECT_NAME(referencing_id)) + ','
FROM sys.sql_expression_dependencies
WHERE referenced_id = c.object_id
AND referenced_minor_id = c.column_id
AND OBJECTPROPERTYEX(referencing_id, 'BaseType') = 'C'
FOR XML PATH('')) ck(check_constraints)
WHERE c.object_id = object_id(@TwoPartTableNameQuoted)
AND c.name = @ColumnNameUnQuoted;
PRINT @DynSQL;
EXEC (@DynSQL);
Find the default constraint with this query here:
SELECT
df.name 'Constraint Name' ,
t.name 'Table Name',
c.NAME 'Column Name'
FROM sys.default_constraints df
INNER JOIN sys.tables t ON df.parent_object_id = t.object_id
INNER JOIN sys.columns c ON df.parent_object_id = c.object_id AND df.parent_column_id = c.column_id
This gives you the name of the default constraint, as well as the table and column name.
When you have that information you need to first drop the default constraint:
ALTER TABLE dbo.YourTable
DROP CONSTRAINT name-of-the-default-constraint-here
and then you can drop the column
ALTER TABLE dbo.YourTable DROP COLUMN YourColumn
The following worked for me against a SQL Azure backend (using SQL Server Management Studio), so YMMV, but, if it works for you, it's waaaaay simpler than the other solutions.
ALTER TABLE MyTable
DROP CONSTRAINT FK_MyColumn
CONSTRAINT DK_MyColumn
-- etc...
COLUMN MyColumn
GO
I got the same:
ALTER TABLE DROP COLUMN failed because one or more objects access this column message.
My column had an index which needed to be deleted first. Using sys.indexes did the trick:
DECLARE @sql VARCHAR(max)
SELECT @sql = 'DROP INDEX ' + idx.NAME + ' ON tblName'
FROM sys.indexes idx
INNER JOIN sys.tables tbl ON idx.object_id = tbl.object_id
INNER JOIN sys.index_columns idxCol ON idx.index_id = idxCol.index_id
INNER JOIN sys.columns col ON idxCol.column_id = col.column_id
WHERE idx.type <> 0
AND tbl.NAME = 'tblName'
AND col.NAME = 'colName'
EXEC sp_executeSql @sql
GO
ALTER TABLE tblName
DROP COLUMN colName
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