src/Query/FluentQuery.php
public function select( $columns ) {

		if ( $columns === Select::ALL ) {

			$this->select->all( $this->alias );

			return $this;
		}

		if ( ! is_array( $columns ) ) {
			$columns = func_get_args();
		}

		foreach ( $columns as $column ) {
			$this->select->also( $this->prepare_column( $column ) );
		}

		$this->select->also( $this->prepare_column( $this->table->get_primary_key() ) );

		$this->focused_select = true;

		return $this;
	}
public function select( $columns ) {

		if ( $columns === Select::ALL ) {

			$this->select->all( $this->alias );

			return $this;
		}

		if ( ! is_array( $columns ) ) {
			$columns = func_get_args();
		}

		foreach ( $columns as $column ) {
			$this->select->also( $this->prepare_column( $column ) );
		}

		$this->select->also( $this->prepare_column( $this->table->get_primary_key() ) );

		$this->focused_select = true;

		return $this;
	}
Select certain columns.

@since 2.0

@param string $columns,...

@return $this