migrations: create symbol_history table

A symbol_history table is added to store precomputed data about the
first version when a symbol is introduced.

For golang/go#37102

Change-Id: I3a36f1da9d2facb795203a8bf9326fe15ca2694c
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/313592
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

migrations/000091_add_symbol_history.down.sql

@@ -0,0 +1,9 @@
+-- Copyright 2021 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+DROP TABLE symbol_history;
+
+END;

migrations/000091_add_symbol_history.up.sql

@@ -0,0 +1,45 @@
+-- Copyright 2021 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+CREATE TABLE symbol_history (
+    id INTEGER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
+    created_at timestamp with time zone DEFAULT CURRENT_TIMESTAMP NOT NULL,
+    updated_at timestamp with time zone DEFAULT CURRENT_TIMESTAMP NOT NULL,
+    package_path_id INTEGER NOT NULL,
+    module_path_id INTEGER NOT NULL,
+    symbol_name_id INTEGER NOT NULL,
+    parent_symbol_name_id INTEGER NOT NULL,
+    package_symbol_id INTEGER NOT NULL,
+    since_version TEXT NOT NULL CHECK(since_version != ''),
+    sort_version text NOT NULL,
+    goos goos NOT NULL,
+    goarch goarch NOT NULL,
+
+    UNIQUE( package_path_id, module_path_id, symbol_name_id, goos, goarch),
+    FOREIGN KEY (package_path_id) REFERENCES paths(id) ON DELETE CASCADE,
+    FOREIGN KEY (module_path_id) REFERENCES paths(id) ON DELETE CASCADE,
+    FOREIGN KEY (symbol_name_id) REFERENCES symbol_names(id) ON DELETE CASCADE,
+    FOREIGN KEY (parent_symbol_name_id) REFERENCES symbol_names(id) ON DELETE CASCADE,
+    FOREIGN KEY (package_symbol_id) REFERENCES package_symbols(id) ON DELETE CASCADE
+);
+
+CREATE TRIGGER set_updated_at BEFORE INSERT OR UPDATE ON symbol_history
+     FOR EACH ROW EXECUTE PROCEDURE trigger_modify_updated_at();
+COMMENT ON TRIGGER set_updated_at ON symbol_history IS
+'TRIGGER set_updated_at updates the value of the updated_at column to the current timestamp whenever a row is inserted or updated to the table.';
+
+CREATE INDEX idx_symbol_history_package_path_id ON symbol_history(package_path_id);
+CREATE INDEX idx_symbol_history_module_path_id ON symbol_history(module_path_id);
+CREATE INDEX idx_symbol_history_symbol_name_id ON symbol_history(symbol_name_id);
+CREATE INDEX idx_symbol_history_parent_symbol_name_id ON symbol_history(parent_symbol_name_id);
+CREATE INDEX idx_symbol_history_package_symbol_id ON symbol_history(package_symbol_id);
+CREATE INDEX idx_symbol_history_goos ON symbol_history(goos);
+CREATE INDEX idx_symbol_history_goarch ON symbol_history(goarch);
+
+COMMENT ON TABLE symbol_history IS
+'TABLE symbol_history documents the first version when a symbol was introduced in a package.';
+
+END;