ADDCOLUMNS() vs SELECTCOLUMNS()

Both functions compute new columns from expressions against a table — the difference is entirely in what happens to the columns that were already there.

ADDCOLUMNS(<table>, <name>, <expression>, ...)
SELECTCOLUMNS(<table>, <name>, <expression>, ...)

ADDCOLUMNS(): Keeps Everything, Adds More

ADDCOLUMNS(Products, "Profit", Products[Price] * 0.3)

The result has every original column from Products — Product, Category, Price — plus the new Profit column tacked on. Nothing from the source table disappears.

SELECTCOLUMNS(): Only What's Listed

SELECTCOLUMNS(Products, "Product", Products[Product], "Profit", Products[Price] * 0.3)

The result has only Product and Profit — Category and Price are gone entirely, not hidden or still-accessible-if-needed. SELECTCOLUMNS() is a reshaping/projection function: it builds a brand new table shape from scratch, and anything not explicitly listed simply isn't part of it.

Source table (Products): Product, Category, Price

ADDCOLUMNS(Products, "Profit", ...)     -> Product, Category, Price, Profit   (everything + new)
SELECTCOLUMNS(Products, "Product", ..., "Profit", ...)  -> Product, Profit    (only what's listed)

Common Mistakes

Expecting SELECTCOLUMNS to Add Like ADDCOLUMNS Does

Reaching for SELECTCOLUMNS() out of habit when the actual goal is "keep everything, plus this one new column" silently drops every column not explicitly re-listed — a nested expression or a later step referencing one of those dropped columns then fails, sometimes confusingly far from where the column actually disappeared.

Forgetting to Re-List a Column SELECTCOLUMNS Still Needs

Every column the result needs to carry forward — including ones just passing through unchanged — has to be explicitly named in SELECTCOLUMNS()'s argument list. There's no shorthand for "this one, unchanged, plus these new ones."

Using ADDCOLUMNS When the Goal Is Actually a Narrow, Reshaped Table

The reverse mistake: ADDCOLUMNS() always keeps the full original column set, which can leave a calculated table or nested table expression carrying far more columns than it actually needs, when SELECTCOLUMNS() would have produced the intended narrower shape from the start.

Best Practices

• Use ADDCOLUMNS() when the goal is "everything that was already there, plus new computed columns."
• Use SELECTCOLUMNS() when the goal is a specific, narrower table shape — and explicitly list every column that needs to survive, including unchanged ones.
• Double-check a SELECTCOLUMNS() call's full argument list whenever a downstream step reports a missing column — it's very often simply not in the list.

Next Steps

• SUMMARIZE()
• Calculated Tables
• CALCULATE
• DAX Function Reference