SQL fundamentals for support staff: SELECT, WHERE, JOIN and reading results safely

Skills you'll practise

• Write a SELECT query that filters with WHERE, sorts with ORDER BY and limits rows predictably
• Identify where NULL values change a filter or a count, and use IS NULL correctly
• Choose between an inner join and a left join for a support question, and calculate how many rows the query will return from sample tables
• Run exploratory queries in a read-only session and recognise statements that change data
• Write a ticket note that records the query, when and where it ran, and the result

Course outline

1. 1.SELECT, WHERE, ORDER BY and LIMITLesson · 14 min
2. 2.NULLs, counting and groupingLesson · 16 min
3. 3.Joining tables: inner join or left join, and how many rows come backLesson · 16 min
4. 4.Exploratory queries in a read-only sessionLesson · 8 min
5. 5.Writing a ticket note that records the query and the resultLesson · 8 min
6. 6.SQL fundamentals for support staff: SELECT, WHERE, JOIN and reading results safely: knowledge checkKnowledge check · 14 questions
7. 7.SQL fundamentals for support staff: SELECT, WHERE, JOIN and reading results safely: practical exerciseKnowledge check · 1 question
8. 8.Final exam10 questions · passing it completes the course, so people who already know the material can test out

Sources it draws on

The lessons and questions are written from these references, so learners can go back to the original.

• PostgreSQL documentation, 2.5 Querying a Table (tutorial)
• PostgreSQL documentation, 2.6 Joins Between Tables (tutorial)
• PostgreSQL documentation, 2.7 Aggregate Functions (tutorial)
• PostgreSQL documentation, 9.21 Aggregate Functions (count(*) vs count(expression); null for no rows)
• PostgreSQL documentation, 9.2 Comparison Functions and Operators (IS NULL)
• PostgreSQL documentation, 7.6 LIMIT and OFFSET
• PostgreSQL documentation, SET TRANSACTION (READ ONLY mode)
• PostgreSQL documentation, 2.9 Deletions (tutorial)