fix load data when escaped and enclosed are the same

.gitattributes

@@ -8,4 +8,5 @@ enginetest/testdata/test6.csv binary
 enginetest/testdata/test7.txt binary
 enginetest/testdata/test8.txt binary
 enginetest/testdata/test9.txt binary
-enginetest/testdata/test10.txt binary
+enginetest/testdata/test10.txt binary
+enginetest/testdata/simple_json.txt binary

enginetest/queries/load_queries.go

@@ -18,6 +18,8 @@ import (
 	"fmt"
 	"time"
 
+	"github.com/dolthub/go-mysql-server/sql/types"
+
 	"github.com/dolthub/go-mysql-server/sql"
 )
 
@@ -126,6 +128,21 @@ var LoadDataScripts = []ScriptTest{
 			},
 		},
 	},
+	{
+		Name: "Load JSON data. EnclosedBy and EscapedBy are the same.",
+		SetUpScript: []string{
+			"create table loadtable(pk int primary key, j json)",
+			"LOAD DATA INFILE './testdata/simple_json.txt' INTO TABLE loadtable FIELDS TERMINATED BY ',' ENCLOSED BY '\"' ESCAPED BY '\"';",
+		},
+		Assertions: []ScriptTestAssertion{
+			{
+				Query: "select * from loadtable",
+				Expected: []sql.Row{
+					{1, types.MustJSON(`{"foo": "bar"}`)},
+				},
+			},
+		},
+	},
 	{
 		Name: "LOAD DATA handles Windows line-endings and a subset of columns that are not in order",
 		SetUpScript: []string{

enginetest/testdata/simple_json.txt

@@ -0,0 +1 @@
+"1","{""foo"":""bar""}"

sql/rowexec/ddl_iters.go

@@ -144,7 +144,7 @@ func (l *loadDataIter) parseFields(ctx *sql.Context, line string) ([]sql.Express
 	// TODO: Support the OPTIONALLY parameter.
 	if l.fieldsEnclosedBy != "" {
 		for i, field := range fields {
-			if string(field[0]) == l.fieldsEnclosedBy && string(field[len(field)-1]) == l.fieldsEnclosedBy {
+			if field[0] == l.fieldsEnclosedBy[0] && field[len(field)-1] == l.fieldsEnclosedBy[0] {
 				fields[i] = field[1 : len(field)-1]
 			} else {
 				return nil, fmt.Errorf("error: field not properly enclosed")
@@ -162,7 +162,22 @@ func (l *loadDataIter) parseFields(ctx *sql.Context, line string) ([]sql.Express
 			} else if field == "\\0" {
 				fields[i] = fmt.Sprintf("%c", 0) // ASCII 0
 			} else {
-				fields[i] = strings.ReplaceAll(field, l.fieldsEscapedBy, "")
+				// The character immediately following the escaped character remains untouched, even if it is the same
+				// as the escape character
+				newField := make([]byte, 0, len(field))
+				for cIdx := 0; cIdx < len(field); cIdx++ {
+					c := field[cIdx]
+					// skip over escaped character, but always add the following character
+					if c == l.fieldsEscapedBy[0] {
+						cIdx += 1
+						if cIdx < len(field) {
+							newField = append(newField, c)
+						}
+						continue
+					}
+					newField = append(newField, c)
+				}
+				fields[i] = string(newField)
 			}
 		}
 	}