mysql: keep REPLACE INTO when generating a :copyfrom LOAD DATA

A :copyfrom query written as REPLACE INTO generated
LOAD DATA LOCAL INFILE '%s' INTO TABLE ..., dropping the REPLACE.
MySQL's default for LOAD DATA is to skip rows that collide on a
primary or unique key, so the upsert the query asked for silently
became a skip.

The parser already reports it (marino ast.InsertStmt.IsReplace), but
nothing read the bit. Carry it on ast.InsertStmt, derive it from the
raw statement in the compiler, add it to plugin.Query, and emit
REPLACE INTO TABLE from the template.

Fixes #4339

Author: hdimer

docs/howto/insert.md

@@ -208,6 +208,10 @@ and use SHOW WARNINGS to check for any problems and roll back if necessary.
 
 Check the [error handling](https://dev.mysql.com/doc/refman/8.0/en/load-data.html#load-data-error-handling) documentation for more information.
 
+Writing the query as `REPLACE INTO` generates `LOAD DATA ... REPLACE INTO TABLE`,
+which overwrites rows that collide on a primary or unique key instead of skipping
+them.
+
 ```sql
 CREATE TABLE foo (a text, b integer, c DATETIME, d DATE);
 

internal/cmd/shim.go

@@ -161,6 +161,7 @@ func pluginQueries(r *compiler.Result) []*plugin.Query {
 			Params:          params,
 			Filename:        q.Metadata.Filename,
 			InsertIntoTable: iit,
+			InsertIsReplace: q.InsertIsReplace(),
 		})
 	}
 	return out

internal/codegen/golang/query.go

@@ -279,6 +279,8 @@ type Query struct {
 	Arg          QueryValue
 	// Used for :copyfrom
 	Table *plugin.Identifier
+	// Used for :copyfrom, true when the query was written as REPLACE INTO
+	InsertIsReplace bool
 }
 
 func (q Query) hasRetType() bool {

internal/codegen/golang/result.go

@@ -218,14 +218,15 @@ func buildQueries(req *plugin.GenerateRequest, options *opts.Options, enums []En
 		}
 
 		gq := Query{
-			Cmd:          query.Cmd,
-			ConstantName: constantName,
-			FieldName:    sdk.LowerTitle(query.Name) + "Stmt",
-			MethodName:   query.Name,
-			SourceName:   query.Filename,
-			SQL:          query.Text,
-			Comments:     comments,
-			Table:        query.InsertIntoTable,
+			Cmd:             query.Cmd,
+			ConstantName:    constantName,
+			FieldName:       sdk.LowerTitle(query.Name) + "Stmt",
+			MethodName:      query.Name,
+			SourceName:      query.Filename,
+			SQL:             query.Text,
+			Comments:        comments,
+			Table:           query.InsertIntoTable,
+			InsertIsReplace: query.InsertIsReplace,
 		}
 		sqlpkg := parseDriver(options.SqlPackage)
 

internal/codegen/golang/templates/go-sql-driver-mysql/copyfromCopy.tmpl

@@ -25,9 +25,16 @@ func convertRowsFor{{.MethodName}}(w *io.PipeWriter, {{.Arg.SlicePair}}) {
 {{end -}}
 // {{.MethodName}} uses MySQL's LOAD DATA LOCAL INFILE and is not atomic.
 //
+{{if .InsertIsReplace -}}
+// Errors are treated as warnings and insertion will continue, even without an
+// error for some cases.  Rows that collide on a primary or unique key replace
+// the existing row.  Use this in a transaction and use SHOW WARNINGS to check
+// for any problems and roll back if you want to.
+{{else -}}
 // Errors and duplicate keys are treated as warnings and insertion will
 // continue, even without an error for some cases.  Use this in a transaction
 // and use SHOW WARNINGS to check for any problems and roll back if you want to.
+{{end -}}
 //
 // Check the documentation for more information:
 // https://dev.mysql.com/doc/refman/8.0/en/load-data.html#load-data-error-handling
@@ -40,7 +47,7 @@ func (q *Queries) {{.MethodName}}(ctx context.Context{{if $.EmitMethodsWithDBArg
 	go convertRowsFor{{.MethodName}}(pw, {{.Arg.Name}})
 	// The string interpolation is necessary because LOAD DATA INFILE requires
 	// the file name to be given as a literal string.
-	result, err := {{if (not $.EmitMethodsWithDBArgument)}}q.{{end}}db.ExecContext(ctx, fmt.Sprintf("LOAD DATA LOCAL INFILE '%s' INTO TABLE {{.TableIdentifierForMySQL}} %s ({{range $index, $name := .Arg.ColumnNames}}{{if gt $index 0}}, {{end}}{{$name}}{{end}})", "Reader::" + rh, mysqltsv.Escaping))
+	result, err := {{if (not $.EmitMethodsWithDBArgument)}}q.{{end}}db.ExecContext(ctx, fmt.Sprintf("LOAD DATA LOCAL INFILE '%s' {{if .InsertIsReplace}}REPLACE {{end}}INTO TABLE {{.TableIdentifierForMySQL}} %s ({{range $index, $name := .Arg.ColumnNames}}{{if gt $index 0}}, {{end}}{{$name}}{{end}})", "Reader::" + rh, mysqltsv.Escaping))
 	if err != nil {
 		return 0, err
 	}

internal/compiler/query.go

@@ -55,6 +55,17 @@ type Query struct {
 	RawStmt *ast.RawStmt
 }
 
+// InsertIsReplace reports whether the query was written as REPLACE INTO. MySQL
+// renders a :copyfrom for such a query as LOAD DATA ... REPLACE INTO TABLE, so
+// that rows colliding on a key overwrite instead of being skipped.
+func (q *Query) InsertIsReplace() bool {
+	if q.RawStmt == nil {
+		return false
+	}
+	ins, ok := q.RawStmt.Stmt.(*ast.InsertStmt)
+	return ok && ins.IsReplace
+}
+
 type Parameter struct {
 	Number int
 	Column *Column

internal/endtoend/testdata/codegen_json/gen/codegen.json

@@ -66389,7 +66389,8 @@
       ],
       "comments": [],
       "filename": "query.sql",
-      "insert_into_table": null
+      "insert_into_table": null,
+      "insert_is_replace": false
     },
     {
       "text": "SELECT id, name, bio FROM authors\nORDER BY name",
@@ -66478,7 +66479,8 @@
       "params": [],
       "comments": [],
       "filename": "query.sql",
-      "insert_into_table": null
+      "insert_into_table": null,
+      "insert_is_replace": false
     },
     {
       "text": "INSERT INTO authors (\n          name, bio\n) VALUES (\n  $1, $2\n)\nRETURNING id, name, bio",
@@ -66630,7 +66632,8 @@
         "catalog": "",
         "schema": "",
         "name": "authors"
-      }
+      },
+      "insert_is_replace": false
     },
     {
       "text": "DELETE FROM authors\nWHERE id = $1",
@@ -66670,7 +66673,8 @@
       ],
       "comments": [],
       "filename": "query.sql",
-      "insert_into_table": null
+      "insert_into_table": null,
+      "insert_is_replace": false
     }
   ],
   "sqlc_version": "v1.31.1",

internal/endtoend/testdata/copyfrom/mysql/go/copyfrom.go

@@ -3,3 +3,6 @@ INSERT INTO foo (a, b, c, d) VALUES (?, ?, ?, ?);
 
 -- name: InsertSingleValue :copyfrom
 INSERT INTO foo (a) VALUES (?);
+
+-- name: ReplaceValues :copyfrom
+REPLACE INTO foo (a, b, c, d) VALUES (?, ?, ?, ?);