Updating mysql table

UPDATE tbl_name SET fld2 = CASE fld1WHEN val1 THEN data1WHEN val2 THEN data2ELSE fld2 ENDThe note is: do not forget ELSE.

If you do not use it, all rows that are outside the range of your updated values will be set to blank!

Only the partitions (or subpartitions) listed are checked for matches, and a row that is not in any of these partitions or subpartitions is not updated, whether it satisfies the clause, are flagged as unsafe for statement-based replication.

updating mysql table-57

Suppose you have a table where each row is associated with a certain group (For example, orders are associated with the customers placing them) where each item WITHIN the group has a distinct number (For example, each person my have a sequence of competition results - each person, therefore, has a 1st, 2nd, 3rd... If you would like to renumber items within their group so that each has the same baseline (say 0), here is an example way to proceed: Create TEMPORARY Table Groups (Id INTEGER AUTO_INCREMENT PRIMARY KEY, Name VARCHAR(31), Group Id VARCHAR(31), Val Within Group INTEGER); INSERT INTO Groups VALUES (null, "Davy", "Boy", 2); INSERT INTO Groups VALUES (null, "Mary", "Girl", 2); INSERT INTO Groups VALUES (null, "Bill", "Boy", 5); INSERT INTO Groups VALUES (null, "Jill", "Girl", -3); INSERT INTO Groups VALUES (null, "Fred", "Boy", 3);# Find the lowest value for each group CREATE TEMPORARY TABLE Group Sum AS SELECT Group Id, MIN(Val Within Group) AS base Val FROM Groups GROUP BY Group Id;# create an index so my SQL can efficiently match ALTER TABLE Group Sum ADD UNIQUE (Group Id);# finally, make the baseline adjustment UPDATE Groups LEFT JOIN Group Sum USING (Group Id) SET Val Within Group=Val Within Group-base Val; SELECT * FROM Groups;# 1 Davy Boy 0# 2 Mary Girl 5# 3 Bill Boy 3# 4 Jill Girl 0# 5 Fred Boy 1#Each group ("Boy", "Girl") now has a (lowest) Val Within Group entry of 0.

Notes: That index addition is necessary because on larger tables my SQL would rather die than figure to (internally) index a single column join.

This will use the SQL UPDATE command with the WHERE clause to update the selected data in the My SQL table tutorials_tbl.

The following example will update the tutorial_title field for a record having the tutorial_id as 3.

when a row of a subset is lost/deleted/moved away from it, the whole subset will need to be reordered.

This can be done similarily : SET @pos=0; UPDATE busstops SET pos = ( SELECT @pos := @pos 1 ) WHERE route = 1 ORDER BY pos ASCChris H (chansel0049) I experienced a weird issue converting from 4 to 5.A is a normal table, B is a temporary table: Worked in 4update A, B set A.population=B.pop_count where A.id=In version 5, however, the above query only updated one element while still matching "all"In 5 I had to do it like this:update A RIGHT JOIN B on A.id=set A.population=B.pop_count Updates all population counts correctly.[edit: RIGHT JOIN not LEFT JOIN...] Related to the post of Mohamed Hossam on May 9 2005 am A more general method to updtate more one row: UPDATE table SET f1='foo', f2= IF(f3=value,‘one’, IF(f3=value_bis,’two’,f2)) WHERE f5='afected' This set the values of field 'f2' according to the values of field 'f3' in the rows field f5 'afected'.Here is a way to use multiple tables in your UPDATE statement, but actually copying one row values into the other, meaning, we're using the same table: UPDATE jobs AS to Table, jobs AS from Table SET to Table.job_type_id = from Table.job_type_id, to Table.job_company_id = from Table.job_company_id, to Table.job_source = from Table.job_source, WHERE (to Table.job_id = 6) AND (from Table.job_id = 1)--------------Pretty cool.If you want to return the value before you updated it without using a seperate select (which unless you lock the table could return a different value than is updated) then you can use a mysql variable like this:update some_table set col = col 1 where key = 'some_key_value' and @value := col The @value := col will always evaluate to true and will store the col value before the update in the @value variable. Additional information on My SQL correlated subqueries is at UPDATE can apparently be used to implement a semaphore (pardon my pseudocode):while TRUE The code above waits until the semaphore is "cleared" (value = 0) and then "sets" it (value = 1).You could then do select @value;in order to see what the value was before you updated it My SQL uses Watcom (Oracle) syntax for UPDATE, so it's possible to write something like:update Table1 t1 join Table2 t2 on t1. When done, you "clear" the semaphore by UPDATE table SET value = 0 WHERE name = 'name' The assumption is that the UPDATE is "atomic" in that no concurrent access by another process can occur between testing and setting the value field.For multiple-table updates, there is no guarantee that assignments are carried out in any particular order. COLUMN2 IS NULLAn outerjoin is performed based on the equijoin condition.

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