1. INTRODUCTION

2. DATA
2.1. SDSS Spectrum
2.2. CRTS
2.3. PTF, iPTF and ZTF
2.4. PanSTARRS
2.5. DECaLS
2.6. Photometric Data Calibration

3. SAMPLE SELECTION
3.1. Preliminary Screening
3.2. Spectral Flux Calibration Problem
3.3. Visual Inspection for EVQs/CLQs
3.4. Spectral Fitting

4. EVQ/CLQ PROPERTIES
4.1. Basic Properties
4.2. Emission Line Properties
4.3. BH Mass
4.4. Eddington Ratio
4.5. Composite Spectra
4.6. Detection Rate

5. DISCUSSIONS
5.1. Decisive Roles for the CL Behavior
5.2. Line Transition Order in CLQs
5.4. Variability Mechanism
5.5. C IV Line Profile

6. CONCLUSIONS