Expressions: Sql expressions with Duckdb (#81666)

duckdb temp storage of dataframes using parquet and querying from sql expressions
---------

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

pkg/expr/sql/parser.go

@@ -0,0 +1,99 @@
+package sql
+
+import (
+	"errors"
+	"strings"
+
+	parser "github.com/krasun/gosqlparser"
+	"github.com/xwb1989/sqlparser"
+)
+
+// TablesList returns a list of tables for the sql statement
+func TablesList(rawSQL string) ([]string, error) {
+	stmt, err := sqlparser.Parse(rawSQL)
+	if err != nil {
+		tables, err := parse(rawSQL)
+		if err != nil {
+			return parseTables(rawSQL)
+		}
+		return tables, nil
+	}
+
+	tables := []string{}
+	switch kind := stmt.(type) {
+	case *sqlparser.Select:
+		for _, t := range kind.From {
+			buf := sqlparser.NewTrackedBuffer(nil)
+			t.Format(buf)
+			table := buf.String()
+			if table != "dual" {
+				tables = append(tables, buf.String())
+			}
+		}
+	default:
+		return nil, errors.New("not a select statement")
+	}
+	return tables, nil
+}
+
+// uses a simple tokenizer
+func parse(rawSQL string) ([]string, error) {
+	query, err := parser.Parse(rawSQL)
+	if err != nil {
+		return nil, err
+	}
+	if query.GetType() == parser.StatementSelect {
+		sel, ok := query.(*parser.Select)
+		if ok {
+			return []string{sel.Table}, nil
+		}
+	}
+	return nil, err
+}
+
+func parseTables(rawSQL string) ([]string, error) {
+	checkSql := strings.ToUpper(rawSQL)
+	if strings.HasPrefix(checkSql, "SELECT") || strings.HasPrefix(rawSQL, "WITH") {
+		tables := []string{}
+		tokens := strings.Split(rawSQL, " ")
+		checkNext := false
+		takeNext := false
+		for _, t := range tokens {
+			t = strings.ToUpper(t)
+			t = strings.TrimSpace(t)
+
+			if takeNext {
+				tables = append(tables, t)
+				checkNext = false
+				takeNext = false
+				continue
+			}
+			if checkNext {
+				if strings.Contains(t, "(") {
+					checkNext = false
+					continue
+				}
+				if strings.Contains(t, ",") {
+					values := strings.Split(t, ",")
+					for _, v := range values {
+						v := strings.TrimSpace(v)
+						if v != "" {
+							tables = append(tables, v)
+						} else {
+							takeNext = true
+							break
+						}
+					}
+					continue
+				}
+				tables = append(tables, t)
+				checkNext = false
+			}
+			if t == "FROM" {
+				checkNext = true
+			}
+		}
+		return tables, nil
+	}
+	return nil, errors.New("not a select statement")
+}