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databases/sql-null-why-two-people-vanish-from-both-your-queries.md
SQL NULL: why two people vanish from both your queries
Two people have no age in your table. You ask for everyone older than 30, then for everyone not older than 30, and the two lists add up to…
databases/sql-joins-how-two-tables-become-one-answer-inner-left-right-full.md
SQL JOINs: how two tables become one answer (INNER, LEFT, RIGHT, FULL)
Your data lives in two tables, but your question needs both. A JOIN lines them up, and the four kinds (INNER, LEFT, RIGHT, FULL) differ…