Eine Einführung in

SQL

To select the data from 20 different columns into one changing the values according to one other column consisting the positions of the 20 columns

MySQL
Sometimes we have un-normailsed data that we want to normalise. Suppose we have data in 20 columns F1 to F20: Line F1 F2 F3 F4 ... ------------------------------ A 11 10 13 15 ... B 20 22 23 28 ... But we want a table that has just one data column. Like this... Line Col Val ---------------- A 1 11 A 2 10 A 3 13 A 4 15 ... B 1 20 B 2 22 B 3 23 B 4 28 ... You can use INSERT ... SELECT ... statement	Execute tidy up code silently DROP TABLE normal Execute set up code DROP TABLE unnormal; CREATE TABLE unnormal (Line CHAR(1) PRIMARY KEY, F1 INTEGER, F2 INTEGER, F3 INTEGER, F4 INTEGER); --Put the bad data in INSERT INTO unnormal VALUES ('A', 11, 10, 13, 15); INSERT INTO unnormal VALUES ('B', 20, 22, 23, 28); --Create the good table CREATE TABLE normal (Line CHAR(1), col INTEGER, val INTEGER, PRIMARY KEY (Line, col) ); --Copy the data into it INSERT INTO normal(Line, col, val) SELECT Line, 1, F1 FROM unnormal UNION SELECT Line, 2, F2 FROM unnormal UNION SELECT Line, 3, F3 FROM unnormal UNION SELECT Line, 4, F4 FROM unnormal; SELECT * FROM normal;
Specific to MySQL
none