![]() SELECT * FROM b JOIN c ON (b.ref = c.id) RIGHT JOIN a ON (a.id = b. Hence my need to check if table (B) exists. My problem arises when there are no records retrieved due to the where conditions thus the table is not created. Often you can express the same thing without extra parentheses by moving the joins around and changing the direction of the outer joins, e.g. After transposing my data I actually save the results into a table(B) so I can join with my main table(A). The a-b join takes effect first, but we can force the b-c join to take effect first by putting it in parentheses, which looks like: SELECT * FROM a LEFT JOIN (b JOIN c ON (b.ref = c.id)) ON (a.id = b.id) In SELECT * FROM a LEFT JOIN b ON (a.id = b.id) JOIN c ON (b.ref = c.id) Remember that you will have to move the ON clauses around so that they stay with their joins-the join in parentheses takes its ON clause with it into the parentheses, so it now comes textually before the other ON clause which will be after the parentheses in the outer join statement. You can put the join expression on the right side in parentheses to cause it to take effect first. Index hints can be specified to affect how the MySQL optimizer makes use of indexes. ![]() See Section 8.2.1.8, Nested Join Optimization. select distinct a.tablename, a.constraintname, b.deleterule, b.updaterule, a.referencedtablename, a.columnname, a.referencedcolumnname, a.tableschema from informationschema.keycolumnusage a join informationschema.referentialconstraints b using (constraintname) where a.tableschema 'databasename' and a.referenced. In general, parentheses can be ignored in join expressions containing only inner join operations. All kinds of outer and normal joins are in the same precedence class and operators take effect left-to-right at a given nesting level of the query. you can find table relations and relations rules.
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