adding notes

Former-commit-id: a71e39a

Author: joncrlsn

notes.md

@@ -0,0 +1,112 @@
+ ==== Constraints
+
+SELECT c.conname AS constraint_name,
+          CASE c.contype
+            WHEN 'c' THEN 'CHECK'
+            WHEN 'f' THEN 'FOREIGN KEY'
+            WHEN 'p' THEN 'PRIMARY KEY'
+            WHEN 'u' THEN 'UNIQUE'
+          END AS "constraint_type",
+          CASE WHEN c.condeferrable = 'f' THEN 0 ELSE 1 END AS is_deferrable,
+          CASE WHEN c.condeferred = 'f' THEN 0 ELSE 1 END AS is_deferred,
+          t.relname AS table_name,
+          array_to_string(c.conkey, ' ') AS constraint_key,
+          CASE confupdtype
+            WHEN 'a' THEN 'NO ACTION'
+            WHEN 'r' THEN 'RESTRICT'
+            WHEN 'c' THEN 'CASCADE'
+            WHEN 'n' THEN 'SET NULL'
+            WHEN 'd' THEN 'SET DEFAULT'
+          END AS on_update,
+          CASE confdeltype
+            WHEN 'a' THEN 'NO ACTION'
+            WHEN 'r' THEN 'RESTRICT'
+            WHEN 'c' THEN 'CASCADE'
+            WHEN 'n' THEN 'SET NULL'
+            WHEN 'd' THEN 'SET DEFAULT'
+          END AS on_delete,
+          CASE confmatchtype
+            WHEN 'u' THEN 'UNSPECIFIED'
+            WHEN 'f' THEN 'FULL'
+            WHEN 'p' THEN 'PARTIAL'
+          END AS match_type,
+          t2.relname AS references_table,
+          array_to_string(c.confkey, ' ') AS fk_constraint_key
+     FROM pg_constraint c
+LEFT JOIN pg_class t  ON c.conrelid  = t.oid
+LEFT JOIN pg_class t2 ON c.confrelid = t2.oid;
+
+
+   SELECT tc.constraint_name
+          , tc.constraint_type
+          , tc.table_name
+          , kcu.column_name
+          , tc.is_deferrable
+          , tc.initially_deferred
+          , rc.match_option AS match_type
+          , rc.update_rule AS on_update
+          , rc.delete_rule AS on_delete
+          , ccu.table_name AS references_table
+          , ccu.column_name AS references_field
+     FROM information_schema.table_constraints tc
+LEFT JOIN information_schema.key_column_usage kcu
+       ON tc.constraint_catalog = kcu.constraint_catalog
+      AND tc.constraint_schema = kcu.constraint_schema
+      AND tc.constraint_name = kcu.constraint_name
+LEFT JOIN information_schema.referential_constraints rc
+       ON tc.constraint_catalog = rc.constraint_catalog
+      AND tc.constraint_schema = rc.constraint_schema
+      AND tc.constraint_name = rc.constraint_name
+LEFT JOIN information_schema.constraint_column_usage ccu
+       ON rc.unique_constraint_catalog = ccu.constraint_catalog
+      AND rc.unique_constraint_schema = ccu.constraint_schema
+      AND rc.unique_constraint_name = ccu.constraint_name
+WHERE tc.constraint_schema = 'public'
+AND tc.constraint_type = 'UNIQUE';
+
+
+ ==== Trigger and Function
+
+SELECT *
+  FROM information_schema.triggers
+   WHERE trigger_schema NOT IN
+          ('pg_catalog', 'information_schema');
+
+
+CREATE TABLE emp (
+    empname text,
+    salary integer,
+    last_date timestamp,
+    last_user text
+);
+
+CREATE FUNCTION emp_stamp() RETURNS trigger AS $emp_stamp$
+    BEGIN
+        -- Check that empname and salary are given
+        IF NEW.empname IS NULL THEN
+            RAISE EXCEPTION 'empname cannot be null';
+        END IF;
+        IF NEW.salary IS NULL THEN
+            RAISE EXCEPTION '% cannot have null salary', NEW.empname;
+        END IF;
+
+        -- Who works for us when she must pay for it?
+        IF NEW.salary < 0 THEN
+            RAISE EXCEPTION '% cannot have a negative salary', NEW.empname;
+        END IF;
+
+        -- Remember who changed the payroll when
+        NEW.last_date := current_timestamp;
+        NEW.last_user := current_user;
+        RETURN NEW;
+    END;
+$emp_stamp$ LANGUAGE plpgsql;
+
+CREATE TRIGGER emp_stamp BEFORE INSERT OR UPDATE ON emp
+    FOR EACH ROW EXECUTE PROCEDURE emp_stamp();
+
+CREATE TRIGGER check_update
+    BEFORE UPDATE ON emp
+    FOR EACH ROW
+    WHEN (OLD.empname IS DISTINCT FROM NEW.empname)
+    EXECUTE PROCEDURE emp_stamp();