SpatiaLite sql

 SpatiaLite 3.0 SQL functions reference list

ST_GeometryN 

list the tables in a SQLite database file 

 SpatiaLite Cookbook

SpatiaLite database tables management with QGis 2.8 

https://github.com/qgis/QGIS/issues/37790 

SELECT * FROM sqlite_master WHERE type='table';

SELECT id, st_astext(st_centroid(st_geometryn(P.geom,1))) FROM '桥墩位置2020-09-29' as P   WHERE id < 10;

--下面的语句没有执行成功
UPDATE '桥墩位置2020-09-29' SET centroid_geom = st_centroid(st_geometryn(geom,1));