kvdb+refactor: move all general sqlite code to seprate dir

In this commit, all the sql, non-postgres-specific, code is moved out of
the postgres package and into a new sqlbase package. This will make it
more easily reusable for future sql integrations.

kvdb/sqlbase/schema.go

@@ -0,0 +1,74 @@
+//go:build kvdb_postgres
+
+package sqlbase
+
+import (
+	"fmt"
+	"strings"
+)
+
+// SQLiteCmdReplacements is a one to one mapping of sqlite keywords that should
+// be replaced by the mapped strings in any command. Note that the sqlite
+// keywords to be replaced are case-sensitive.
+type SQLiteCmdReplacements map[string]string
+
+func newKVSchemaCreationCmd(table, schema string,
+	replacements SQLiteCmdReplacements) string {
+
+	var (
+		tableInSchema = table
+		finalCmd      string
+	)
+	if schema != "" {
+		finalCmd = fmt.Sprintf(
+			`CREATE SCHEMA IF NOT EXISTS ` + schema + `;`,
+		)
+
+		tableInSchema = fmt.Sprintf("%s.%s", schema, table)
+	}
+
+	// Construct the sql statements to set up a kv table in postgres. Every
+	// row points to the bucket that it is one via its parent_id field. A
+	// NULL parent_id means that the key belongs to the uppermost bucket in
+	// this table. A constraint on parent_id is enforcing referential
+	// integrity.
+	//
+	// Furthermore, there is a <table>_p index on parent_id that is required
+	// for the foreign key constraint.
+	//
+	// Finally, there are unique indices on (parent_id, key) to prevent the
+	// same key being present in a bucket more than once (<table>_up and
+	// <table>_unp). In postgres, a single index wouldn't enforce the unique
+	// constraint on rows with a NULL parent_id. Therefore, two indices are
+	// defined.
+	//
+	// The replacements map can be used to replace any sqlite keywords.
+	// Callers should note that the sqlite keywords are case-sensitive.
+	finalCmd += fmt.Sprintf(`
+CREATE TABLE IF NOT EXISTS ` + tableInSchema + `
+(
+    key BLOB NOT NULL,
+    value BLOB,
+    parent_id BIGINT,
+    id INTEGER PRIMARY KEY,
+    sequence BIGINT,
+    CONSTRAINT ` + table + `_parent FOREIGN KEY (parent_id)
+        REFERENCES ` + tableInSchema + ` (id)
+        ON UPDATE NO ACTION
+        ON DELETE CASCADE
+);
+CREATE INDEX IF NOT EXISTS ` + table + `_p
+    ON ` + tableInSchema + ` (parent_id);
+CREATE UNIQUE INDEX IF NOT EXISTS ` + table + `_up
+    ON ` + tableInSchema + `
+    (parent_id, key) WHERE parent_id IS NOT NULL;
+CREATE UNIQUE INDEX IF NOT EXISTS ` + table + `_unp 
+    ON ` + tableInSchema + ` (key) WHERE parent_id IS NULL;
+`)
+
+	for from, to := range replacements {
+		finalCmd = strings.Replace(finalCmd, from, to, -1)
+	}
+
+	return finalCmd
+}