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MySQL Conditional Insert

... If your DBMS does not impose limitations on which table you select from when you execute an insert, try: INSERT INTO x_table(instance, user, item) SELECT 919191, 123, 456 FROM dual WHERE NOT EXISTS (SELECT * FROM x_table WHE...
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HTML table with fixed headers?

Is there a cross-browser CSS/JavaScript technique to display a long HTML table such that the column headers stay fixed on-screen and do not scroll with the table body. Think of the "freeze panes" effect in Microsoft Excel. ...
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Difference between one-to-many and many-to-one relationship

... From this page about Database Terminology Most relations between tables are one-to-many. Example: One area can be the habitat of many readers. One reader can have many subscriptions. One newspaper can have many subscriptions. A Many to One relation is the same as o...
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Multiple select statements in Single query

... SELECT ( SELECT COUNT(*) FROM user_table ) AS tot_user, ( SELECT COUNT(*) FROM cat_table ) AS tot_cat, ( SELECT COUNT(*) FROM course_table ) AS tot_course share ...
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Adding a new SQL column with a default value

... Try this: ALTER TABLE table1 ADD COLUMN foo INT DEFAULT 0; From the documentation that you linked to: ALTER [ONLINE | OFFLINE] [IGNORE] TABLE tbl_name alter_specification [, alter_specification] ... alter_specification: ... ...
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Postgresql - change the size of a varchar column to lower length

I have a question about the ALTER TABLE command on a really large table (almost 30 millions rows). One of its columns is a varchar(255) and I would like to resize it to a varchar(40) . Basically, I would like to change my column by running the following command: ...
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How do you copy a record in a SQL table but swap out the unique id of the new row?

...es close to what I need, but my scenario is slightly different. The source table and destination table are the same and the primary key is a uniqueidentifier (guid). When I try this: ...
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Convert Rows to columns using 'Pivot' in SQL Server

I have read the stuff on MS pivot tables and I am still having problems getting this correct. 8 Answers ...
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Physical vs. logical / soft delete of database record?

...and you don't have to worry about cascading a delete through various other tables in the database that reference the row you are deleting. Disadvantage is that you have to code any reporting/display methods to take the flag into account. As far as if it is a common practice - I would say yes, but ...
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How to find foreign key dependencies in SQL Server?

... all Foreign Key Relationships within the current database. SELECT FK_Table = FK.TABLE_NAME, FK_Column = CU.COLUMN_NAME, PK_Table = PK.TABLE_NAME, PK_Column = PT.COLUMN_NAME, Constraint_Name = C.CONSTRAINT_NAME FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS C INNER JOIN INF...