A sliding valve has a valve body, a sliding sleeve received in a longitudinal bore of the valve body, and a collet receivable in a longitudinal bore of the sliding sleeve. The valve body has one or more fluid ports on an uphole portion of the sidewall thereof. The sliding sleeve is movable between an uphole closed position closing the one or more fluid ports and a downhole open position opening the one or more fluid ports.The sliding sleeve has a sleeve-profile formed at least by one or more sleeve-grooves and one or more sleeve-ridges longitudinally distributed on an inner surface thereof. The collet has a flexible collet-profile formed by at least one or more collet-grooves and one or more collet-ridges respectively corresponding to the sleeve-grooves and sleeve-ridges. The length of each sleeve-ridge or collet-ridge is smaller than that of corresponding sleeve-groove or collet-groove.