ExprToColumnLabelVisitor.java

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package org.apache.doris.analysis;

/**
 * Visitor that produces the column-label string for any {@link Expr}.
 *
 * <p>For all expression types except {@link SlotRef}, the result is identical
 * to {@link ExprToSqlVisitor} (i.e. the standard SQL string).  For
 * {@link SlotRef} the result is the raw column name without table qualification
 * or backtick quoting, matching the legacy {@code SlotRef.toColumnLabel()}
 * behaviour.
 *
 * <p>Usage:
 * <pre>
 *     String label = expr.accept(ExprToColumnLabelVisitor.INSTANCE, null);
 * </pre>
 */
public class ExprToColumnLabelVisitor extends ExprVisitor<String, Void> {

    /** Singleton — the visitor is stateless. */
    public static final ExprToColumnLabelVisitor INSTANCE = new ExprToColumnLabelVisitor();

    private ExprToColumnLabelVisitor() {
    }

    /**
     * Default: delegate to {@link ExprToSqlVisitor} for every expression type
     * that does not need special column-label handling.
     */
    @Override
    public String visit(Expr expr, Void context) {
        return ExprToSqlVisitor.INSTANCE.visit(expr, null);
    }

    /**
     * For a {@link SlotRef} the column label is the raw column name only
     * (no table prefix, no backtick quoting), matching the legacy
     * {@code SlotRef.toColumnLabel()} override that simply returned {@code col}.
     */
    @Override
    public String visitSlotRef(SlotRef expr, Void context) {
        return expr.col;
    }
}