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craigmbooth/matrix_multiply.sql

Created May 18, 2013 16:13
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Sparse matrix multiply in SQL
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matrix_multiply.sql
-- Join columns to rows, group by rows and columns, then filter to get the cell you want.
SELECT A.row_num, B.col_num, SUM(A.value*B.value)
FROM A,B
WHERE A.col_num=B.row_num
GROUP BY A.row_num, B.col_num;
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