Error parsing base SELECT expression

```
1> {ok, Ast, _} = sql_lex:string("SELECT 1").
{ok,[{'SELECT',1},{'INTNUM',1,"1"}],1}
2> sqlparse:parse(Ast).
{error,{1,sqlparse,["syntax error before: ",[]]}}
3> {ok, Ast, _} = sql_lex:string("SELECT 1+2+3+4*1.2").
{ok,[{'SELECT',1},
{'INTNUM',1,"1"},
{'+',1},
{'INTNUM',1,"2"},
{'+',1},
{'INTNUM',1,"3"},
{'+',1},
{'INTNUM',1,"4"},
{'*',1},
{'APPROXNUM',1,"1.2"}],
1}
4> sqlparse:parse(Ast).
{error,{1,sqlparse,["syntax error before: ",[]]}}
```

Start by reproducing the examples with sql_lex:string("SELECT 1") and sqlparse:parse(Ast), then inspect the parser entry point and grammar handling for SELECT expressions. Done means the shown base SELECT and arithmetic expression inputs parse successfully without syntax errors.

Written by the indexing model from the issue text.