Sql updating table from same table
If you update a column that has been declared , an error occurs if strict SQL mode is enabled; otherwise, the column is set to the implicit default value for the column data type and the warning count is incremented.The implicit default value is tables for which there are foreign key constraints, the My SQL optimizer might process tables in an order that differs from that of their parent/child relationship.
Say that table D had an additional column that was not defined with a default value: Not everyone realizes that you can explicitly specify NULL in the values list of an INSERT statement.But you can also update whole sets of records at once, and in very powerful ways. For example, you can delete rows in one table depending on whether or not they exist in another table.SQL even has a way, a relatively new addition to the standard, by which you can insert, update, and delete all at once. For example, you want to insert a new record into the DEPT table.The syntax for inserting a single row is consistent across all database brands.As a shortcut, you can omit the column list in an INSERT statement: of the columns in the table, and be mindful of the order of the values in the VALUES list; you must supply values in the same order in which the database displays columns in response to a SELECT * query.