How Can I Efficiently Combine Multiple SELECT Statements with LIMIT to Retrieve One Row from Each Schema?

Combining Multiple SELECT Statements

To retrieve data from multiple schemas in a single query, you can combine multiple SELECT statements using the UNION operator. However, when using LIMIT to return only one row from each schema, you may encounter issues with discarding the remaining rows.

To resolve this issue, ensure that the individual SELECT sub-queries are wrapped in parentheses:

(SELECT result FROM schema1.table LIMIT 1) UNION ALL
(SELECT result FROM schema2.table LIMIT 1)
(SELECT result FROM schema3.table LIMIT 1)

By enclosing the sub-queries in parentheses, the LIMIT and ORDER BY clauses will apply to each sub-query individually, preventing the discarding of rows from other schemas.

The UNION ALL operator combines the results of the individual queries, eliminating duplicate rows. It's important to use UNION ALL because it preserves the order of the results, which is important in this case where you want one row for each schema.

Once you have combined the SELECT statements, you can copy the results back into Excel against the corresponding schema names. This will provide you with a single column result with as many rows as there are schemas, as desired.

The above is the detailed content of How Can I Efficiently Combine Multiple SELECT Statements with LIMIT to Retrieve One Row from Each Schema?. For more information, please follow other related articles on the PHP Chinese website!