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This option takes a list of one or more partitions or subpartitions (or both).
So, I do it in one "magick" query ;)Here an example:"3" is a some value, from form or somethingupdate item set rate = case when round((rate 3)/2) You sometimes run into the problem that you want to replace a substring occuring in a column with a different string, without touching the rest of the string.
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.
If you wish to use an increment based on subset of a table you may combine UPDATE with Variables:e.g.
A table that contains entries of different categories, in which an internal order needs to represented ( lets say a table with busstops on different routes).
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.
If you set a column to the value it currently has, My SQL notices this and does not update it. Records not matching the equijoin from table2 are marked with null.
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!
(Bug #11758262, Bug #50439) See Section 18.104.22.168, “Determination of Safe and Unsafe Statements in Binary Logging”, for more information.
If you access a column from the table to be updated in an expression, assignments are generally evaluated from left to right.
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.