UPDATE SomeTable SET p_key = CASE WHEN p_key = 'a' THEN 'b' WHEN p_key = 'b' THEN 'a' ELSE p_key END WHERE p_key IN ('a', 'b'); 1. 2. 3. 4. 5. 5、场景五:表之间的数据匹配 WHEN 后的条件中嵌套子查询的 IN 和 EXISTS 谓词 需求:根据 CourseMaster 表和 OpenCourse 表...
Whenever you set up a script to create or drop an index, you want a safety check in there. Drop the index if it exists. Create the index if it doesn’t. Or do something else programmatically. Checking if an index exists is a pretty frequent task. But there’s no simple function to ...
ALTER TABLE Departments ADD CONSTRAINT CHK_PID CHECK (ID>=1 AND PID >=0); -- remove check ALTER TABLE Departments DROP CHECK CHK_PID; 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 如果属于数据库逻辑,比如:审计,外键可以使用触发器 CREATE TABLE IF NOT EXISTS `department` ( `id` i...
SQL 2005+EXECUTE master.sys.sp_MSforeachdb 'USE [?]; if exists(select * from INFORMATION_SCHEMA.tables where TABLE_TYPE=''BASE TABLE'' and TABLE_NAME=''DB_BACKUP_LOG_T'') begin print ''exist in '' + db_name() end'SQL 2000...
CREATE TABLE IF NOT EXISTS equivalent in SQL Server, Since this is the top question for this topic in Google even though it has been closed: if not exists (select * from sys.tables t join sys.schemas s on (t.schema_id = s.schema_id) where s.name = 'myschema' and t.name = '...
WHERE table_schema='dbo' AND table_name='student' ) SELECT 1 ELSE SELECT 0; In this query, we use theIF EXISTScondition in SQL Server to check if the specified table exists in the schema. If the subquery returns a result, it returns 1; otherwise, it returns 0. ...
In this article, we saw how to check whether a column exists within a table. Overall, we worked with three different DBMSs: MSSQL MySQL PostgreSQL Each system has unique methods for performing the checks. Generally,these methods make use of metadata queries. Such checks help ensure database ...
CREATE FUNCTION dbo.CheckSequenceKey (@SequenceKey nvarchar(10)) RETURNS bit AS BEGIN DECLARE @retval bit IF EXISTS (SELECT 1 FROM dbo.Seqs S WHERE S.SequenceKey = @SequenceKey) SET @retval = 1 ELSE SET @retval = 0 RETURN @retval END; GO ALTER TABLE dbo.Sometbl ADD...
Applies to:SQL ServerAzure SQL DatabaseAzure SQL Managed Instance Checks the integrity of a specified constraint or all constraints on a specified table in the current database. Transact-SQL syntax conventions Syntax syntaxsqlคัดลอก ...
(SQL Server 2000 only.) Shows the text that is displayed to the user whenever a row that violates the constraint is entered. Check existing data on creation When selected, this option ensures that all data that exists in the table before the constraint was created is verified against the...