The associated absorption features in quasar spectra of the Sload
  Digital Sky survey .I. \MgII\ absorption doublets
  Using the SDSS spectra of quasars included in the DR7Q or DR12Q catalogs, we
search for Mg II narrow absorption doublets in the spectra data around Mg II
emission lines. We obtain 17,316 Mg II doublets, within the redshift range of
0.3299<= z_abs <= 2.5663. We find that a velocity offset of v_r < 6000 km/s is
a safe boundary to constrain the vast majority of associated Mg II systems,
although we find some doublets at v_r > 6000 km/s. If associated Mg II
absorbers are defined by v_r < 6000 km/s, ~33.3% of the absorbers supposed to
be contaminants of intervening systems. Removing the 33.3% contaminants, ~4.5%
of the quasars present at least one associated Mg II system with
W_r\lambda2796>=0.2 \AA. The fraction of associated Mg II systems with high
velocity outflows correlates with the average luminosities of their central
quasars, indicating a relationship between outflows and the quasar feedback
power. The v_r distribution of the outflow Mg II absorbers is peaked at 1023
km/s, which is smaller than the corresponding value of the outflow C IV
absorbers. The redshift number density evolution of absorbers (dn/dz) limited
by v_r > -3000 km/s differs from that of absorbers constrained by v_r > 2000
km/s. While, absorbers limited by v_r > 2000 km/s and higher values exhibit
similar profile of dn/dz. In addition, the dn/dz is smaller when absorbers are
constrained with larger v_r. The distributions of equivalent widths, and the
ratio of W_r\lambda2796/W_r\lambda2803 is the same for associated and
intervening systems, and independent on quasar luminosity.
