SQLZOO, 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

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

Postgres
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	Run the tidy code silently Run set up code --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 Postgres
none

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