Sql updating a table from the same table
If you access a column from the table to be updated in an expression, assignments are generally evaluated from left to right.For multiple-table updates, there is no guarantee that assignments are carried out in any particular order.If you set a column to the value it currently has, My SQL notices this and does not update it.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.I am trying to fix an issue for a customer which requires us to update a column in a table with the value in the column concatenated (
Use the WHEN clause to prevent the trigger from firing for every insert and update.There are 3 syntaxes for the UPDATE statement depending on whether you are performing a traditional update or updating one table with data from another table. all I have a situation where I have to check for insert on a table or change for a perticular field in the table and populate two other fields of the same table.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. Instead, update a single table and rely on the provides to cause the other tables to be modified accordingly. COLUMN2 IS NULLAn outerjoin is performed based on the equijoin condition.Now my question is that, that i want to update db Unique column of this table, such that db Unique should contain Id of Table1 where is Unique is 1 in all duplicate rows based on col2,col3,col4 & col5 So my updated data will look like this The important part to notice is that you are joining the table to itself but differentiating selection criteria on the "sides" of the join.