We can also add theUNIQUEconstraint to an existing column using theALTER TABLEcommand. For example, For a Single Column -- add unique constraint to an existing columnALTERTABLECollegesADDUNIQUE(college_id); Here, the SQL command adds theUNIQUEconstraint to thecolleges_idcolumn in the existingColl...
mysql>ALTER TABLE `table_name` ADD INDEX index_name ( `column` ) FULLTEXT(全文索引) ALTER TABLE `table_name...它与前面的”普通索引”类似,不同的就是:索引列的值必须唯一,但允许有空值。如果是组合索引,则列值的组合必须唯一。...它有以下几种创建方式: (1)创建索引:CREATE UNIQUE INDEX index...
SQL UNIQUE Constraint on ALTER TABLE To create a UNIQUE constraint on the "ID" column when the table is already created, use the following SQL: MySQL / SQL Server / Oracle / MS Access: ALTERTABLEPersons ADDUNIQUE(ID); To name a UNIQUE constraint, and to define a UNIQUE constraint on mu...
其中TABLE 是表名,COLUMN 是自增的那一列的名字,例如: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 SELECT setval('user_id_seq', (SELECT max(id) FROM "user")); 如果执行以上的sql语句报错 ERROR: currval of sequence “user_id_seq” is not yet defined in this session 那么最开始执行 ...
SqlUpdateDeleteSpecificationBase SqlUpdateMergeAction SqlUpdateSpecification SqlUpdateStatement SqlUserDefinedDataTypeNullState SqlUserDefinedScalarFunctionCallExpression SqlUseStatement SqlValuesInsertMergeActionSource SqlVariableAssignment SqlVariableColumnAssignment ...
ADD COLUMN to variable table? Add prefix in data column Add Time in SQL HH:MM:SS to another HH:MM:SS Adding a column to a large (100 million rows) table with default constraint adding a extra column in a pivot table created uisng T-SQL Pivot Table query Adding a partition scheme ...
组合索引ALTER TABLE `table_name` ADD INDEX index_name ( `column1`, `column2`, `column3` ) Mysql各种索引区别: 普通索引(INDEX):最基本的索引,没有任何限制 唯一索引(UNIQUE):与"普通索引"类似,不同的就是:索引列的值必须唯一,但允许有空值。
SQL Server Unique constraint for values in different columnI agree 100% with the above comments ...
SQL Copy USE AdventureWorks2022; GO CREATE TABLE Production.TransactionHistoryArchive2 ( TransactionID int NOT NULL, CONSTRAINT AK_TransactionID UNIQUE(TransactionID) ); GO Create a unique constraint on a nullable column In Object Explorer, connect to an instance of Database Engine. On the Stan...
コピー -- Return the name of unique constraint. SELECT name FROM sys.objects WHERE type = 'UQ' AND OBJECT_NAME(parent_object_id) = N' DocExc'; GO -- Delete the unique constraint. ALTER TABLE dbo.DocExc DROP CONSTRAINT UNQ_ColumnB_DocExc; GO 詳細...