"Immigrant", a novella by Clifford D. Simak, first published in Astounding Science Fiction, March 1954, available at the Internet Archive. You might have read it in one of these compilations.
People enter a contest to win a chance to go to this wonderful planet.
Kimon was a galactic El Dorado, a never-never land, the country at the rainbow's foot. There were few who did not dream of going there, and there were many who aspired, but those who were chosen were a very small percentage of those who tried to make the grade and failed.
[. . . .]
You did not go to Kimon simply because you wished to go there; you worked to go to Kimon.
First of all, you had to have the specified IQ rating and that ruled out ninety-nine per cent or better of Earth's population. Once you had passed the IQ test, you settled down to grueling years of study, and at the end of the years of study you wrote an examination and, once again, most of the aspirants were ruled out. Not more than one in a thousand who took the examinations passed.
Year after year, Earthmen and women dribbled out to Kimon, settled there, prospered, wrote their letters home.
Of those who went out, none came back. Once you had lived on Kimon, you could not bear the thought of going back to Earth.
He asks the robot bartender to unmake a drink. The bar complains that it can't unmake a cocktail.
"Here," he said to the cabinet, "have a drink on me."
He set the glass, still full, on the top of the cabinet.
The cabinet gurgled in surprise.
"I do not drink," it said.
"Then take it back and put it in the bottle."
"I can't do that," said the cabinet, horrified. "It's already mixed."
"Separate it, then."
"It can't be separated," wailed the cabinet. "Surely you don't expect me—"
There was a little swish and Maxine stood in the center of the room.
She smiled at Bishop.
"What goes on?" she asked.
The cabinet wailed at her. "He wants me to unmix a drink. He wants me to separate it, the liquor from the mix. He knows I can't do that."
"My, my," she said, " I thought you could do anything."
"I can't unravel a drink," the cabinet said primly. "Why don't you take it off my hands?"
The story concludes with a voice saying, "You should go to bed. You don't want to be late for school".
The cabinet said, "You'd better get off to bed, sir."
"I suppose I should," said Bishop. "It's been a long, hard day."
"You'll want to get up early," said the cabinet, "so you aren't late for school."