/
select.go
165 lines (135 loc) · 3.58 KB
/
select.go
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package parser
import (
"github.com/asdine/genji/sql/query"
"github.com/asdine/genji/sql/scanner"
)
// parseSelectStatement parses a select string and returns a Statement AST object.
// This function assumes the SELECT token has already been consumed.
func (p *Parser) parseSelectStatement() (query.SelectStmt, error) {
var stmt query.SelectStmt
var err error
// Parse field list or query.Wildcard
stmt.Selectors, err = p.parseResultFields()
if err != nil {
return stmt, err
}
// Parse "FROM".
var found bool
stmt.TableName, found, err = p.parseFrom()
if err != nil || !found {
return stmt, err
}
// Parse condition: "WHERE EXPR".
stmt.WhereExpr, err = p.parseCondition()
if err != nil {
return stmt, err
}
// Parse order by: "ORDER BY fieldRef [ASC|DESC]?"
stmt.OrderBy, stmt.OrderByDirection, err = p.parseOrderBy()
if err != nil {
return stmt, err
}
// Parse limit: "LIMIT EXPR"
stmt.LimitExpr, err = p.parseLimit()
if err != nil {
return stmt, err
}
// Parse offset: "OFFSET EXPR"
stmt.OffsetExpr, err = p.parseOffset()
if err != nil {
return stmt, err
}
return stmt, nil
}
// parseResultFields parses the list of result fields.
func (p *Parser) parseResultFields() ([]query.ResultField, error) {
// Parse first (required) result field.
rf, err := p.parseResultField()
if err != nil {
return nil, err
}
rfields := []query.ResultField{rf}
// Parse remaining (optional) result fields.
for {
if tok, _, _ := p.ScanIgnoreWhitespace(); tok != scanner.COMMA {
p.Unscan()
return rfields, nil
}
if rf, err = p.parseResultField(); err != nil {
return nil, err
}
rfields = append(rfields, rf)
}
}
// parseResultField parses the list of result fields.
func (p *Parser) parseResultField() (query.ResultField, error) {
// Check if the * token exists.
if tok, _, _ := p.ScanIgnoreWhitespace(); tok == scanner.MUL {
return query.Wildcard{}, nil
}
p.Unscan()
e, lit, err := p.parseExpr()
if err != nil {
return nil, err
}
rf := query.ResultFieldExpr{Expr: e, ExprName: lit}
// Check if the AS token exists.
if tok, _, _ := p.ScanIgnoreWhitespace(); tok == scanner.AS {
rf.ExprName, err = p.parseIdent()
if err != nil {
return nil, err
}
return rf, nil
}
p.Unscan()
return rf, nil
}
func (p *Parser) parseFrom() (string, bool, error) {
if tok, _, _ := p.ScanIgnoreWhitespace(); tok != scanner.FROM {
p.Unscan()
return "", false, nil
}
// Parse table name
ident, err := p.parseIdent()
return ident, true, err
}
func (p *Parser) parseOrderBy() (query.FieldSelector, scanner.Token, error) {
// parse ORDER token
if tok, _, _ := p.ScanIgnoreWhitespace(); tok != scanner.ORDER {
p.Unscan()
return nil, 0, nil
}
// parse BY token
if tok, pos, lit := p.ScanIgnoreWhitespace(); tok != scanner.BY {
return nil, 0, newParseError(scanner.Tokstr(tok, lit), []string{"BY"}, pos)
}
// parse field reference
ref, err := p.parseFieldRef()
if err != nil {
return nil, 0, err
}
// parse optional ASC or DESC
if tok, _, _ := p.ScanIgnoreWhitespace(); tok == scanner.ASC || tok == scanner.DESC {
return query.FieldSelector(ref), tok, nil
}
p.Unscan()
return query.FieldSelector(ref), 0, nil
}
func (p *Parser) parseLimit() (query.Expr, error) {
// parse LIMIT token
if tok, _, _ := p.ScanIgnoreWhitespace(); tok != scanner.LIMIT {
p.Unscan()
return nil, nil
}
e, _, err := p.parseExpr()
return e, err
}
func (p *Parser) parseOffset() (query.Expr, error) {
// parse OFFSET token
if tok, _, _ := p.ScanIgnoreWhitespace(); tok != scanner.OFFSET {
p.Unscan()
return nil, nil
}
e, _, err := p.parseExpr()
return e, err
}