  Hydrogen emissions of RR Lyrae variables are the imprints of shock waves
traveling through their atmospheres. We develop a pattern recognition
algorithm, which is then applied to single-epoch spectra of SDSS and LAMOST.
These two spectroscopic surveys covered $\sim$ 10,000 photometrically confirmed
RR Lyrae stars. We discovered in total 127 RR Lyrae stars with blueshifted
Balmer emission feature, including 103 fundamental mode (RRab), 20
first-overtone (RRc), 3 double-mode (RRd), and 1 Blazhko type (temporary
classification for RR Lyrae stars with strong Blazhko modulation in Catalina
sky survey that cannot be characterized) RR Lyrae variable. This forms the
largest database to date of the properties of hydrogen emission in RR Lyrae
variables. Based on ZTF DR5, we carried out a detailed light-curve analysis for
the Blazhko type RR Lyrae star with hydrogen emission of long-term modulations.
We characterize the Blazhko type RR Lyrae star as an RRab and point out a
possible Blazhko period. Finally, we set up simulations on mock spectra to test
the performance of our algorithm and on the real observational strategy to
investigate the occurrence of the "first apparition".
