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--- postgresqlfunctions [2024/03/04 16:48] – [Arrays] z0hpvk
+++ postgresqlfunctions [2025/03/08 22:24] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
-===== pl/pgsql =====
+===== SQL and PL/pgSQL =====
+==== JSON ====
+[[https://cdn.sanity.io/files/sczeoy4w/production/065818a8cd88cd048137368e5710ec35c0361185.pdf|| JSON Cheat Sheet]]
 ==== Arrays ====
+Arrays can be displayed as ''ARRAY[1,2,3]'' or ''{1,2,3}''.\\
 === Operators ===
@@ Line 54: / Line 59: @@
 === Conversion ===
 <code SQL>
-SELECT array_to_string(ARRAY[1,2,3], ',');
+SELECT array_to_string(ARRAY[1,2,3], ',');         -- Returns 1 row (1,2,3)
-SELECT unnest(ARRAY[1,2,3]);
+SELECT unnest(ARRAY[1,2,3]);                       -- Returns 3 rows
-SELECT generate_subscripts(ARRAY['A','B','C'], 1); == Returns 3 rows (1,2,3)
+SELECT generate_subscripts(ARRAY['A','B','C'], 1); -- Returns 3 rows
+--Convert text column with comma separated values to array
+ALTER TABLE name_basics ALTER primaryprofession TYPE text[]
+                        USING string_to_array(primaryprofession, ',');
+</code>
+==== Hierarchical Data ====
+<code SQL>
+WITH RECURSIVE t1(n) AS (
+  VALUES (0)
+  UNION ALL
+  SELECT n+1 FROM t1 WHERE n < 5)
+SELECT * FROM t1;
+</code>
+<code SQL>
+CREATE TABLE family (key int, parent_key int, name text);
+INSERT INTO family VALUES (1, null, 'Grandad');
+INSERT INTO family VALUES (2, 1, 'Dad');
+INSERT INTO family VALUES (3, 2, 'Tracy');
+INSERT INTO family VALUES (4, 2, 'Ian');
+INSERT INTO family VALUES (5, 3, 'Michaela');
+INSERT INTO family VALUES (6, 3, 'Joshua');
+INSERT INTO family VALUES (7, 5, 'Freya');
+INSERT INTO family VALUES (8, 1, 'Colin');
+INSERT INTO family VALUES (9, 8, 'Mark');
+INSERT INTO family VALUES (10, 8, 'Simon');
+</code>
+<code SQL>
+WITH RECURSIVE a AS (
+  SELECT key, parent_key, name, 1::integer level, ARRAY[key] path, ' ' indent,
+         CASE WHEN EXISTS (SELECT 1 FROM family f2 WHERE f2.parent_key = f1.key )
+		      THEN 0 ELSE 1 END is_leaf
+  FROM   family f1
+  WHERE  parent_key IS NULL
+  UNION ALL
+  SELECT b.key, b.parent_key, a.indent || b.name, a.level +1, array_append(a.path, b.key), a.indent || ' ',
+         CASE WHEN EXISTS (SELECT 1 FROM family f2 WHERE f2.parent_key = b.key )
+		      THEN 0 ELSE 1 END is_leaf
+  FROM   family b
+  JOIN   a ON a.key = b.parent_key )
+SELECT key, parent_key, name, level, path, is_leaf FROM a ORDER BY path;
 </code>