| 摘要 |
PROBLEM TO BE SOLVED: To permit index retrieval without being aware of nest structure of a merging table. SOLUTION: A from phrase processing means 1000 inspects whether or not there is a merging table from a head of a perspective tree outputted by an SQL(Structured Query Language) analysis part. Once the merging table is detected, a merging table processing means 1100 is called to recursively process the merging table on the perspective tree. An external merging table processing means 1200 and an internal merging table processing means 1300 are called by the merging table processing means 1100 in the case of external merging and internal merging in a start table of the merging table to discriminate a position where a merging condition is present on the perspective tree and the kind of merging, thereby searching for the position to which the merging condition is moved and a table where a null value should be set when the merging condition is not met. A merging condition setting means 1400 is called by the external merging table processing means 1200 or internal merging table processing means 1300 to set the merging condition set in the start table to an object table to be processed and when the merging condition is not met, preparations for setting the null value in the object table to be processed are made on condition that the null value should be set.
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