Find the SQL. Understand the result.

SQLPathLab uses MySQL 8.0 by default and helps you find complete queries, real results, and common mistakes.

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Site examples use MySQL 8.0 by default. Material dialect differences are called out only where needed.

Quick start

Start from a common task

SELECTSelects the columns or expressions returned by a query.WHEREFilters rows so only records matching a condition are returned.LEFT JOINKeeps all rows from the left table and adds matching right-table data.GROUP BYGroups rows by one or more columns for aggregation.CASE WHENReturns different values based on conditions.ROW_NUMBERAssigns a continuous number to rows after ordering or partitioning.DATE_FORMATFormats a date or datetime value as a specific string.INChecks whether a value exists in a list or subquery result.

Common SQL

Frequently used syntax

Practical SQL Guides

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SQL clause order and logical executionUnderstand the logical order of FROM, WHERE, GROUP BY, HAVING, SELECT, and ORDER BY.Why NULL and three-valued logic cause errorsNULL is not an empty string, and comparisons with NULL can be UNKNOWN.The real difference between WHERE and HAVINGWHERE filters source rows; HAVING filters groups after aggregation.Why JOIN creates duplicates or missing rowsDiagnose JOIN row-count changes through result grain, key uniqueness, and unmatched rows.LEFT JOIN filters in ON versus WHEREThe location of a right-table predicate determines whether unmatched left rows remain.COUNT(*), COUNT(column), and COUNT DISTINCTThe three forms answer row count, non-NULL value count, and unique-value count.