Got rid of sql dependency in schema package

go/libraries/doltcore/schema/schema.go

@@ -17,7 +17,6 @@ package schema
 import (
 	"strings"
 
-	"github.com/dolthub/go-mysql-server/sql"
 	"gopkg.in/src-d/go-errors.v1"
 
 	"github.com/dolthub/dolt/go/libraries/doltcore/schema/typeinfo"
@@ -49,7 +48,13 @@ type Schema interface {
 
 	// AddColumn adds a column to this schema in the order given and returns the resulting Schema.
 	// The new column cannot be a primary key. To alter primary keys, create a new schema with those keys.
-	AddColumn(column Column, order *sql.ColumnOrder) (Schema, error)
+	AddColumn(column Column, order *ColumnOrder) (Schema, error)
+}
+
+// ColumnOrder is used in ALTER TABLE statements to change the order of inserted / modified columns.
+type ColumnOrder struct {
+	First       bool   // True if this column should come first
+	AfterColumn string // Set to the name of the column after which this column should appear
 }
 
 // ColFromTag returns a schema.Column from a schema and a tag

go/libraries/doltcore/schema/schema_impl.go

@@ -20,8 +20,6 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/dolthub/go-mysql-server/sql"
-
 	"github.com/dolthub/dolt/go/store/types"
 )
 
@@ -287,7 +285,7 @@ func (si *schemaImpl) Checks() CheckCollection {
 	return si.checkCollection
 }
 
-func (si schemaImpl) AddColumn(newCol Column, order *sql.ColumnOrder) (Schema, error) {
+func (si schemaImpl) AddColumn(newCol Column, order *ColumnOrder) (Schema, error) {
 	if newCol.IsPartOfPK {
 		return nil, fmt.Errorf("cannot add a column with that is a primary key: %s", newCol.Name)
 	}

go/libraries/doltcore/sqle/alterschema.go

@@ -85,7 +85,7 @@ func addColumnToTable(
 		return nil, err
 	}
 
-	newSchema, err := oldSchema.AddColumn(newCol, order)
+	newSchema, err := oldSchema.AddColumn(newCol, orderToOrder(order))
 	if err != nil {
 		return nil, err
 	}
@@ -99,6 +99,16 @@ func addColumnToTable(
 	return newTable.AddColumnToRows(ctx, newColName, newSchema)
 }
 
+func orderToOrder(order *sql.ColumnOrder) *schema.ColumnOrder {
+	if order == nil {
+		return nil
+	}
+	return &schema.ColumnOrder{
+		First:       order.First,
+		AfterColumn: order.AfterColumn,
+	}
+}
+
 func createColumn(nullable Nullable, newColName string, tag uint64, typeInfo typeinfo.TypeInfo, defaultVal, comment string) (schema.Column, error) {
 	if nullable {
 		return schema.NewColumnWithTypeInfo(newColName, tag, typeInfo, false, defaultVal, false, comment)