SQL Update

Use Sql Update to change values in a table.

You can do it on a single-row, group of rows or all rows. The new data can be a constant value or an expression using certain function.

The syntax to update data in a table:

UPDATE table_name
SET column_name=expression,column_name=expression, . . .
WHERE conditions

If there is a WHERE condition in the Update statement, it is a good idea to test the condition first. To do that , apply the Where condition into the Sql Select statement. Verify that the result from that Sql select is the rows that you want to update. That way you can feel confident that you are changing the correct rows.

Let's use our previous table as an example. We are supposed to change the value of column B in table Tbl_L for ID number 2. Currently the value is 50 and we want to change it into 55.

This is the statement:

UPDATE tbl_L
SET B = 55
WHERE ID = 2

Let's use this simple example to show how to verify the WHERE conditions. To do this, change the UPDATE into SELECT * FROM and remove the SET statement. Leave the WHERE conditions.

Now, this is what we got:

SELECT * FROM  tbl_L
SET B = 55>   <--remove this statement
WHERE ID = 2

Run the Sql statement, and verify that the result is what you expected. If it is then run the Update statement.

The syntax to update data in a table with the value from other table:

UPDATE table2
SET    table2.price = table1.price
FROM   table2
       INNER JOIN table1
         ON ( table2.rowid = table1.rowid ); 
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