Postgres 10

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CREATE TABLE pricetorentratio (_2010_10 TEXT)

CREATE TABLE

INSERT INTO pricetorentratio VALUES ('8.74 ')

INSERT 0 1

INSERT INTO pricetorentratio VALUES ('')

INSERT 0 1

ALTER table pricetorentratio 

ALTER column _2010_10 type numeric USING (trim(_2010_10)::numeric);

ERROR:  invalid input syntax for type numeric: ""

    ALTER table pricetorentratio 
    ALTER column _2010_10 type numeric USING (NULLIF(trim(_2010_10),'')::numeric);

ALTER TABLE

SELECT *
FROM pricetorentratio

_2010_10

8.74

null

SELECT 2