private void ParseWhereClause(SelectStatement s)
{
if (_tokens.LookAhead().TokenType != TokenType.KW_WHERE) return;
_tokens.Read();
ExpressionList l = ParseExprList();
if (l.Count < 1) {
throw new Exception("The expression is missing from the WHERE clause.");
}
s.WhereClause = new WhereClause(l);
}
private void ParseSelectClause(SelectStatement s)
{
bool wildcard = false;
bool distinct = false;
switch (_tokens.LookAhead().TokenType) {
case TokenType.KW_DISTINCT:
_tokens.Read();
distinct = true;
break;
case TokenType.OP_MUL:
_tokens.Read();
wildcard = true;
break;
case TokenType.KW_ALL:
_tokens.Read();
distinct = false;
break;
}
if (wildcard && _tokens.LookAhead().TokenType != TokenType.KW_FROM) {
throw new Exception("SELECT syntax error. No result columns specified. Near \"" + _tokens.LookAhead().Lexeme.StringValue() + "\"");
}
ExpressionList l = null;
if (!wildcard) {
l = ParseColumnList();
if (l.Count == 0) {
throw new Exception("SELECT syntax error. No result columns specified.");
}
}
s.SelectClause = new SelectClause(l, wildcard, distinct);
}
private Expression ParseSelectStatement()
{
if (_tokens.LookAhead().TokenType != TokenType.KW_SELECT) return null;
_tokens.Read();
SelectStatement s = new SelectStatement();
ParseSelectClause(s);
ParseFromClause(s);
ParseWhereClause(s);
ParseGroupByClause(s);
ParseOrderByClause(s);
ParseLimitClause(s);
return s;
}
private void ParseOrderingTerms(SelectStatement s)
{
ExpressionList l = new ExpressionList();
//match exp (ASC|DESC) (, exp (ASC|DESC))*
while (true) {
ParseExpression();
if (_exprs.Count < 1) {
throw new Exception("The base expression is missing.");
}
Expression e = _exprs.Pop();
switch (_tokens.LookAhead().TokenType) {
case TokenType.KW_ASC:
_tokens.Read();
l.Add(new OrderingTerm(e, SortOrder.ASCENDING));
break;
case TokenType.KW_DESC:
_tokens.Read();
l.Add(new OrderingTerm(e, SortOrder.DESCENDING));
break;
default:
l.Add(new OrderingTerm(e, SortOrder.ASCENDING));
break;
}
if (_tokens.LookAhead().TokenType != TokenType.PM_COMMA) { break; }
else {
_tokens.Read();
}
}
s.OrderByClause = new OrderByClause(l);
}
private void ParseOrderByClause(SelectStatement s)
{
if (_tokens.LookAhead().TokenType != TokenType.KW_ORDER) return;
_tokens.Read();
if (_tokens.LookAhead().TokenType != TokenType.KW_BY) {
throw new Exception("ORDER BY clause syntax error.");
}
_tokens.Read();
ParseOrderingTerms(s);
}
private void ParseLimitClause(SelectStatement s)
{
if (_tokens.LookAhead().TokenType != TokenType.KW_LIMIT) return;
_tokens.Read();
ParseExpression();
if (_exprs.Count < 1) {
throw new Exception("The expression for the LIMIT clause was missing.");
}
s.LimitClause = new LimitClause(_exprs.Pop());
if (_tokens.LookAhead().TokenType != TokenType.KW_OFFSET) return;
_tokens.Read();
ParseExpression();
if (_exprs.Count < 1) {
throw new Exception("The expression for the OFFSET clause was missing.");
}
s.LimitClause.Offset = _exprs.Pop();
}
private void ParseGroupByClause(SelectStatement s)
{
if (_tokens.LookAhead().TokenType != TokenType.KW_GROUP) return;
_tokens.Read();
if (_tokens.LookAhead().TokenType != TokenType.KW_BY) {
throw new Exception("GROUP BY clause syntax error.");
}
_tokens.Read();
ExpressionList l = ParseExprList();
if (l.Count == 0) {
throw new Exception("The expression is missing from the GROUP BY clause.");
}
s.GroupByClause = new GroupByClause(l);
if (_tokens.LookAhead().TokenType != TokenType.KW_HAVING) return;
_tokens.Read();
ParseExpression();
if (_exprs.Count < 1) {
throw new Exception("The expression is missing from the HAVING clause.");
}
s.GroupByClause.HavingClause = new HavingClause(_exprs.Pop());
}
private void ParseFromClause(SelectStatement s)
{
if (_tokens.LookAhead().TokenType != TokenType.KW_FROM) return;
_tokens.Read();
ExpressionList l = ParseColumnList();
if (l.Count == 0) {
throw new Exception("FROM syntax error. No table expressions specified.");
}
s.FromClause = new FromClause(l);
}
