Practical case Analysis of mysql Multi-table query

This article mainly introduces the actual case analysis of mysql multi-table query, the content of the article is carefully selected and edited by the author, has a certain pertinence, and is of great significance to everyone's reference, the following is to understand the actual case study of mysql multi-table query with the author.

# case: select city employees who work in Toronto

SELECT last_name,job_id,e.department_id,department_nameFROM employees AS eJournal published AS d journal AS lWHERE e.`department _ id` = d.`department _ id`and d.`location _ id` = l.`location _ id`AND l.citybaby toronto'

# case; query the number of countries with more than 2 departments under each country

SELECT country_id, COUNT (*) FROM locations AS l.`location _ id` = d.`location _ id`GROUP BY country_idHAVING

COUNT (*) > 2

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