Data normalization
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.
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
DROP TABLE normal
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;
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