Backend support for database IF NOT EXISTS

cmd/influxd/run/server_test.go

@@ -52,10 +52,30 @@ func TestServer_DatabaseCommands(t *testing.T) {
 				exp:     `{"results":[{"error":"database already exists"}]}`,
 			},
 			&Query{
-				name:    "drop database should succeed",
+				name:    "create database should not error with existing database with IF NOT EXISTS",
+				command: `CREATE DATABASE IF NOT EXISTS db0`,
+				exp:     `{"results":[{}]}`,
+			},
+			&Query{
+				name:    "create database should create non-existing database with IF NOT EXISTS",
+				command: `CREATE DATABASE IF NOT EXISTS db1`,
+				exp:     `{"results":[{}]}`,
+			},
+			&Query{
+				name:    "show database should succeed",
+				command: `SHOW DATABASES`,
+				exp:     `{"results":[{"series":[{"name":"databases","columns":["name"],"values":[["db0"],["db1"]]}]}]}`,
+			},
+			&Query{
+				name:    "drop database db0 should succeed",
 				command: `DROP DATABASE db0`,
 				exp:     `{"results":[{}]}`,
 			},
+			&Query{
+				name:    "drop database db1 should succeed",
+				command: `DROP DATABASE db1`,
+				exp:     `{"results":[{}]}`,
+			},
 			&Query{
 				name:    "show database should have no results",
 				command: `SHOW DATABASES`,

meta/statement_executor.go

@@ -89,6 +89,9 @@ func (e *StatementExecutor) ExecuteStatement(stmt influxql.Statement) *influxql.
 
 func (e *StatementExecutor) executeCreateDatabaseStatement(q *influxql.CreateDatabaseStatement) *influxql.Result {
 	_, err := e.Store.CreateDatabase(q.Name)
+	if err == ErrDatabaseExists && q.IfNotExists {
+		err = nil
+	}
 	return &influxql.Result{Err: err}
 }