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Introduction In PostgreSQL, Tuple comparison (row/tuple comparison) and Multi-column IN (IN condition on multiple columns) are two extremely powerful features that help write concise, clearer SQL queries and significantly optimize performance compared to manually chaining multiple AND/OR conditions. Tuple comparison Tuple comparison allows grouping multiple columns or values into a tuple (using parentheses (...)) and comparing these two tuples directly with each other using operators like =, <>, <, >, <=, >= Used for Keyset Pagination with more than 1 column and sorting applied Lexicographical order PostgreSQL compares elements from left to right, similar to dictionary sorting, starting by comparing the first pair of elements. If they differ, the result of the entire comparison is decided immediately without evaluating subsequent columns If they are equal, it proceeds to compare the next pair of elements, continuing this process until the end. General Example (a, ...

Introduction When performing a table join that compares multiple columns simultaneously (such as ON A.col1 = B.col1 AND A.col2 = B.col2), PostgreSQL will still use familiar algorithms like Hash Join, Merge Join or Nested Loop Join. However, the way these algorithms process multiple columns involves very distinctive strategies as follows. Hash Join This is usually the number one choice for Postgres when joining multiple columns on large tables. Instead of hashing each individual column, Postgres performs string concatenation to hash the combination of all those columns at the same time. Build Phase: Postgres takes the values of all participating join columns and groups them together (like combining value = col1 + col2 + col3), then inputs this entire combined string into the Hash Function to calculate the Hash Number to be placed into the Bucket. Probe Phase: Next, it also combines the corresponding columns of the remaining table to hash similarly and then compares it with the Hash Tabl...

Introduction A Composite Index is an index type that contains two or more columns on the same table. It includes the following characteristics A Composite Index can be created for a maximum of 32 columns This is the default configuration according to the INDEX_MAX_KEYS constant of Postgres In practice, you should not create an index with more than 3 to 4 columns because it increases the index size, slowing down INSERT/UPDATE/DELETE operations The column order is sorted ascendingly by default However, unlike a standard index where you can sort ascending or descending at will, when using a Composite Index, you can only sort the columns all ascending, all descending or in the exact order specified at creation time For example, when using ON table (c1, c2) (default is all ascending), then You can query ORDER BY c1 ASC, c2 ASC You can query ORDER BY c1 DESC, c2 DESC But the index will not work with the query ORDER BY c1 ASC, c2 DESC Operation Order When using a Composite Index, you must ...