iffyio commented on code in PR #1467:
URL:
https://github.com/apache/datafusion-sqlparser-rs/pull/1467#discussion_r1801494903
##########
src/parser/mod.rs:
##########
@@ -11173,12 +11173,36 @@ impl<'a> Parser<'a> {
self.peek_token().location
)
}
- expr => self
- .parse_optional_alias(keywords::RESERVED_FOR_COLUMN_ALIAS)
- .map(|alias| match alias {
- Some(alias) => SelectItem::ExprWithAlias { expr, alias },
- None => SelectItem::UnnamedExpr(expr),
- }),
+ expr => {
+ // Parse a [`SelectItem`] based on an [MsSql] syntax that uses
the equal sign
+ // to denote an alias, for example: SELECT col_alias = col
FROM tbl
+ // [MsSql]:
https://learn.microsoft.com/en-us/sql/t-sql/queries/select-examples-transact-sql?view=sql-server-ver16#b-use-select-with-column-headings-and-calculations
+ let expr = if self.dialect.supports_eq_alias_assigment() {
+ if let Expr::BinaryOp {
+ ref left,
+ op: BinaryOperator::Eq,
+ ref right,
+ } = expr
+ {
+ if let Expr::Identifier(alias) = left.as_ref() {
+ return Ok(SelectItem::ExprWithAlias {
+ expr: *right.clone(),
+ alias: alias.clone(),
+ });
+ }
+ }
+ expr
+ } else {
+ expr
+ };
+
+ // Parse the common AS keyword for aliasing a column
+ self.parse_optional_alias(keywords::RESERVED_FOR_COLUMN_ALIAS)
+ .map(|alias| match alias {
+ Some(alias) => SelectItem::ExprWithAlias { expr, alias
},
+ None => SelectItem::UnnamedExpr(expr),
+ })
Review Comment:
this works as its own match clause for example:
```rust
Expr::BinaryOp {
left,
op: BinaryOperator::Eq,
right,
} if self.dialect.supports_eq_alias_assigment() &&
matches!(left.as_ref(), Expr::Identifier(_)) => {
let Expr::Identifier(alias) = *left else {
return parser_err!(
"BUG: expected identifier expression as alias",
self.peek_token().location
);
};
Ok(SelectItem::ExprWithAlias {
expr: *right,
alias,
})
}
```
I think the least desirable option involves the expression cloning, i.e. the
`right.clone()` I think we want to avoid in any case
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